Okay, I finally found why I couldn't use my SSH.
It is a, in my opinion, really dumb problem. My $HOME-dir
had the mode 775 (drwxrwxr-x) instead of 755 (drwxr-xr-x).
That is apparently a silent problem. No errors/logs said
anything more than something along the lines of
Pubkey authentication failed: Permission denied.
It should, in my opinion, say something along the lines of
Authentication failed: improper permissions. (See https://link.to/solution/or/problem).
And the link would tell you what permission shit needs to be.
Anyways, I solved it with a simple chmod 755 /home/$USERNAME.
Well, good night.
// BurnyLlama