I can't help as I don't have exp with tmux or brew;
but I do know that if you crosspost your post/question into c/linux you'll have a better time finding someone that knows how to help!🤗

What's the value of your $TERM variable?

Unironically try turning your computer off and on again.

Tmux settings are global and persistent. Just deleting your config files is insufficient. You have to kill the server and restart it. Uninstalling and reinstalling will not kill a running tmux server. tmux kill-server should work too.

Now if it persists across reboots, then there must be a file still lingering somewhere. If you are sure your home directory is clean you can try searching whatever you installed in /etc.

This is all assuming you're trying to go back to a clean slate and failing. If the borked status bar is the result of your current .tmux.conf, then you'll have to post that.

Feels like a font issue. Do you have e.g. nerdfont installed and in use in your terminal? You could check the config for plugins that makes that style, and check which fonts are in use. Could also be powerline fonts that are needed: https://github.com/powerline/fonts

It was exactly that. The stupid thing is: I usually shut down my Mac at the end of my workday and on the next day and start everything I need via script and always got funny looks from my co-workers because "you can just close it and keep it running" so I tried it a few days and honestly did not think about restarting because it would have been a fresh start before.

But now I know there's a tmux server running that I can kill when problems occur and I won't need to reboot Everytime tmux starts acting funny. So at least I learned from being dumb and not thinking about basic trouble shooting steps...

Reinstall or install from a different source?

Just ditch your .tmux.conf and use oh my tmux. It should have everything you're looking for.