I have already completely uninstalled and re-downloaded the client, but the result is the same.
The graphics card is fine, in case anyone here is thinking “your GPU is broken”.
Aaaah there was some cache left.
I emptied the entire cache of the normal user and reloaded TeamSpeak.
Now it works again and the update to Beta77 could be installed without any problems.
By the way: You have Kernel 5 installed, I have Kernel 6.