I’ve been running kde plasma on my Debian 12 desktop for a few month and until now i haven’t run into any problems. When i rebooted my computer today and everything was normal until login. When i got to the black loading screen with the kde logo it was normal for about 30 seconds. After that the loading symbol froze and i gained control of the mouse however i wasn’t able to do anything with it.
I experienced similar problem and later figured out it was caused by my firewall misconfiguration which prevented loopback traffic so you might want to check that.
I would recommend launching a TTY session and observe the journal for anything that may be causing the issue.
You could also try creating a new user account and see if the problem continues to persist.
I have made some minor changes to my firewall recently. Could you give me some more details about the issue you encountered?
What’s your firewall environment?
nftables, iptables or something else? which firewall software do you use?
For some reason it seems that if i log into gnome then log out and then log into kde it loads fine.