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)
I hate to admit it but perhaps it is not such a bad advice...
For my personal curiosity, how on Earth did you end up uninstalling lightdm and using startx? Did you follow a tutorial? Where do you even get this kind of advice?
For future reference what you did is not for beginners and it would have messed up any distro. It has nothing to do with Manjaro.
Try an immutable distro, maybe that will stand up better to this kind of thing.
I didn't uninstall lightdm. I was under the impression that startx would just start the GUI, regardless of what "engine" it's running on.
startx makes a new X server, which uses the programs you put in ~/.xinitrc and the X server depends on the first program in there that runs in the foreground. If that program dies it doesn't start, the X server doesn't either.