Open your wsl ubuntu terminal

install open-ssh server

sudo apt update 
sudo apt install openssh-server

Configure the ssh server: sudo vim /etc/ssh/sshd_config

1. PermitRootLogin no - disallows root login for security
2. PasswordAuthentication yes - if you want to allow password login
3. PubkeyAuthentication yes - if you want to use key-based authentication (recommended)
4. Port 2222 - Windows ssh server already uses port 22, so we need to pick a different one.
5. ListenAddress 0.0.0.0

Activate and start the ssh server:

sudo systemctl start ssh
sudo systemctl enable ssh

Set mirrored networking mode in .wslconfig

[wsl2]
networkingMode=mirrored

Expose port 2222 in the wsl2 firewall in PRIVILEGED PowerShell terminal:

New-NetFirewallHyperVRule -Name "SSH" -DisplayName "SSH" -Direction Inbound -VMCreatorId '{40E0AC32-46A5-438A-A0B2-2B479E8F2E90}' -Protocol TCP -LocalPorts 2222

Restart wsl by shutting it down (wsl --shutdown) and then starting it again (wsl)

Generate new ssh keys on your remote machine by following this guide from GitHub

Add your keys to your wsl's user ~/.ssh/authorized_keys

1. Copy the contents of the public key you created in step 1.
2. Run: public_key_placeholder >> ~/.ssh/authorized_keys - make sure to replace public_key_placeholder with the actual contents of the public key

[Optional] Add ssh config

1. Edit your ssh config file: vim ~/.ssh/config
2. Add the following config (make sure to replace placeholder values):

Host wsl_hostname_placeholder
  Hostname wsl_hostname_placeholder
  Port 2222
  User wsl_user_placheolder
  UseKeychain yes
  AddKeysToAgent yes
  IdentityFile ~/.ssh/id_rsa

Now you can ssh to your wsl2 instance: ssh wsl_hostname_placeholder

1. If you didn't add a ssh config, then you need specify those options: ssh wsl_user_placheolder@wsl_hostname_placeholder -p 2222