The official manuals are fine and translated into many languages. But yeah the wiki isn’t great.

First, check if you can login, with your new user, on the Linux console (i.e. Ctrl-Alt-F1 through F7). If you can, the username change probably went through correctly. Report back if you cannot login via console or you get warnings/errors.

Your login session does automatically terminate if the session process for Cinnamon exits, booting you back to GDM (or whatever login manager you have). So probably the Cinnamon session process, started by GDM, craps out for some reason. The reason is probably, I suspect, that it cannot access or cannot find some file it wants to open.

Check ~/.xsession-errors, it might tell you what went wrong.

Also check the permissions of your home folder, the files in your home folder, and check if you correctly set up the symbolic link from /home/olduser to /home/newuser as the guide suggests.

There’s a browser extension called “Your Codecs.” which can prevent YouTube from serving you AV1-encoded videos.

It’s like the old Debian but with newer software.

I guess the wayland stuff works ok now. That wasn’t quite ready for the mainstream in the last release.

dist-upgrade is a lot faster and easier, and is usually well tested