This is a small guide on resolving an issue I was having that prevented me from installing libc6-dev. The issue I was having was as such:
libc6-dev : Depends: libc6 (= 2.35-0ubuntu3) but 2.35-0ubuntu3.1 is to be installed
The libc6-dev package wants to install version 2.35-0ubuntu3, which is (very slightly) "older" than the libc6 package I have installed at version 2.35-0ubuntu3.1 (notice the .1). This basically prevents me from installing libc6-dev which in turn prevents me from installing build-essential. You need build-essential to do a lot of development work, such as compiling C code.
Here is the process I went through, from discovering the problem to solving it, but let's start with the solution straight up.