EDIT: I kinda solved it by installing Wayland (with Nvidia card, Ouch!) to replace Xorg. Not sure if this is gonna last though. Perhaps Manjaro is the one I'm gonna throw out FIRST if anything happens from now on.
What should be the first line of defense? Timeshift?
This happened after I installed AUR package masterpdfeditor and 2 applications from github (some hashing algorithm programs, I think they were "Dilithium" and "Latice-based-cryptography-main", one of them was provided by NIST.)
If using GUI: I login, black screen for few seconds, then back at login screen.
If going to ctrl+alt+f2, login successful, then startx, see picture provided (higher quality).
I tried adding a new user, but result is the same.
I have a live usb to do the Timeshift. (I can also chroot if necessary... But I'm not extremely professional)
https://forum.endeavouros.com/t/graphical-session-doesnt-start-first-time-invalid-mit-magic-cookie-1/5947/8
Check
/etc/hostnameThis is based on the image, the best you can do it check the logs like other comments said, it's better if the error is identified through the log.
It's not about the host name. They clearly have invalid mappings in their ~/.Xmodmap (if you'd care to look at the picture).
My comment is based on
MIT-MAGIC-COOKIE-1from the log in the picture. Look at it again and there's alsoSocketCreateListener() failed. So OP may check this as wellhttps://wiki.archlinux.org/title/xorg#SocketCreateListener_error