Hi Stefan,
I am a absolute Newbie.
Yes, your right, everything works correct.
I download teamviewer, then a install policykit-1 and then teamviewer over the terminal.

I thought in the desktop environment software like teamviewer or anydesk would be installable.

Regards Arthur

deb http://deb.debian.org/debian bookworm main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm main contrib non-free-firmware

deb http://deb.debian.org/debian bookworm-updates main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free-firmware

# deb http://deb.debian.org/debian bookworm-backports main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free-firmware

deb http://security.debian.org/debian-security bookworm-security main contrib non-free-firmware
# deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free-firmware

I was having this exact issue after installing the Debian 12 minimal,

after running "sudo nano /etc/apt/sources.list"

weirdly enough, i was met with only one line which was:

deb cdrom:[Debian GNU/Linux 12.11.0 _Bookworm_ - Official amd64 NETINST with firmware 20250517-09:51]/ bookworm contrib main non-free-firmware

from past experiences, this was not normal specially on a fresh install, so i ended up here, and used @alipour66m 's comment, it fixed my issue. all i had to do was to comment out the first line like so

#deb cdrom:[Debian GNU/Linux 12.11.0 _Bookworm_ - Official amd64 NETINST with firmware 20250517-09:51]/ bookworm contrib main non-free-firmware

my "/etc/apt/sources.list" ended looking like this;

# deb cdrom:[Debian GNU/Linux 12.11.0 _Bookworm_ - Official amd64 NETINST with firmware 20250517-09:51]/ bookworm contrib main non-free-firmware

deb http://deb.debian.org/debian bookworm main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm main contrib non-free-firmware

deb http://deb.debian.org/debian bookworm-updates main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free-firmware

# deb http://deb.debian.org/debian bookworm-backports main contrib non-free-firmware
# deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free-firmware

deb http://security.debian.org/debian-security bookworm-security main contrib non-free-firmware
# deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free-firmware

deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

deb http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

deb http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware

deb http://deb.debian.org/debian bookworm-proposed-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-proposed-updates main contrib non-free non-free-firmware

you have several repeated repositories 14 and 87

# === Stable Release (Bookworm) ===
deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

# Stable Point Release Updates
deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

# Stable Security Updates
deb http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

# Stable Backports (newer packages backported)
deb http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware

# Stable Proposed Updates (testing updates before stable release)
deb http://deb.debian.org/debian bookworm-proposed-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-proposed-updates main contrib non-free non-free-firmware


# === Testing Release (Trixie) ===
deb http://deb.debian.org/debian testing main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian testing main contrib non-free non-free-firmware

# Testing Updates (rarely used, sometimes temporary)
deb http://deb.debian.org/debian testing-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian testing-updates main contrib non-free non-free-firmware

# Testing Backports (uncommon)
deb http://deb.debian.org/debian testing-backports main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian testing-backports main contrib non-free non-free-firmware

# Testing Proposed Updates
deb http://deb.debian.org/debian testing-proposed-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian testing-proposed-updates main contrib non-free non-free-firmware


# === Unstable Release (Sid) ===
deb http://deb.debian.org/debian unstable main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian unstable main contrib non-free non-free-firmware

# Unstable Backports (very rare, mostly unused)
deb http://deb.debian.org/debian unstable-backports main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian unstable-backports main contrib non-free non-free-firmware


# === Experimental (Bleeding Edge) ===
deb http://deb.debian.org/debian experimental main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian experimental main contrib non-free non-free-firmware


# === Security Archive for Old Releases ===
deb http://archive.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src http://archive.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware


# === Debian Archive (Old Releases and Point Snapshots) ===
deb http://archive.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://archive.debian.org/debian bookworm main contrib non-free non-free-firmware


# === Snapshots Archive (Reproducible Builds / Historical State) ===
deb http://snapshot.debian.org/archive/debian/ bookworm main contrib non-free non-free-firmware
deb-src http://snapshot.debian.org/archive/debian/ bookworm main contrib non-free non-free-firmware


# === Debug Symbol Packages (Debugging and Analysis) ===
deb http://deb.debian.org/debian-debug bookworm-debug main contrib non-free
deb-src http://deb.debian.org/debian-debug bookworm-debug main contrib non-free


# === Volatile Updates (Historical, mostly phased out) ===
deb http://volatile.debian.org/debian-volatile bookworm main contrib non-free
deb-src http://volatile.debian.org/debian-volatile bookworm main contrib non-free


# === Special-Purpose Mirrors / Mirrors with CDN ===
deb https://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

deb https://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

deb https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

deb https://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware


# === Experimental Snapshots (Rare, used by developers) ===
deb http://snapshot.debian.org/archive/debian/ experimental main contrib non-free non-free-firmware
deb-src http://snapshot.debian.org/archive/debian/ experimental main contrib non-free non-free-firmware

=== Stable Release (Bookworm) ===

deb https://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

Stable Point Release Updates

deb https://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

Stable Security Updates

deb https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src https://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

Stable Backports (newer packages backported)

deb https://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian bookworm-backports main contrib non-free non-free-firmware

=== Testing Release (Trixie) ===

deb https://deb.debian.org/debian testing main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian testing main contrib non-free non-free-firmware

Testing Updates

deb https://deb.debian.org/debian testing-updates main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian testing-updates main contrib non-free non-free-firmware

Testing Backports

deb https://deb.debian.org/debian testing-backports main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian testing-backports main contrib non-free non-free-firmware

Testing Proposed Updates

deb https://deb.debian.org/debian testing-proposed-updates main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian testing-proposed-updates main contrib non-free non-free-firmware

=== Unstable Release (Sid) ===

deb https://deb.debian.org/debian unstable main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian unstable main contrib non-free non-free-firmware

=== Experimental (Bleeding Edge) ===

deb https://deb.debian.org/debian experimental main contrib non-free non-free-firmware
deb-src https://deb.debian.org/debian experimental main contrib non-free non-free-firmware

=== Debug Symbol Packages ===

deb https://deb.debian.org/debian-debug bookworm-debug main contrib non-free
deb-src https://deb.debian.org/debian-debug bookworm-debug main contrib non-free

Fixed