Linux

ah classic mistake of installing AUR packages on manjaro. been there done that. check your logs and search for errors, it probably overwrote/deleted some xorg config that you must either manually add back or regenerate. sorry i can't help further im a linux noobie but that was my issue when this happened to me.

Most stable Manjaro experience

Start by not using Manjaro. Seriously this won't be the first time this happens to you. It's not a great distro. Consider EndevourOS if you want Arch without the command line install.

One of your steps should be to throw Manjaro in the trash and install EndeavourOS instead.

If you have it setup timeshift should work...

But please know that the AUR + Manjaro is not a supported or recommend combination. The AUR is intended to be used with the official Arch repos; Manjaro repos are often weeks or sometimes even up to a month behind. Even the Manjaro devs put a warning for this reason.
Not only that, the Manjaro base packages often aren't even built with the same flags as Arch base packages; which is probably what happened here.
Consider using EndeavorOS or archinstall , else this won't be the last time something like this happens.

Manjaro is not up-to-date with Arch repos. Using AUR in Manjaro is a huge mistake.

If you wanna use AUR, I suggest you to go all in with Arch itself

However I still recommend you to use AUR as less as possible, cause too many AUR can mess even with Arch

I'm not usually one to blame the distro but... as another comment here has stated, "Most stable manjaro experience". Try EndeavorOS, it's manjaro but not bad.

Have you checked the log files under /var/log/xorg.0....log?

Also see https://wiki.archlinux.org/title/Xorg#Troubleshooting

If you want to get your graphical session back quickly, maybe try setting up GNOME with wayland (https://wiki.archlinux.org/title/GNOME#Wayland_sessions)

Don't use startx to start X, use the display manager: systemctl restart lightdm

Ok so clearly none of the people commenting here have even bothered to look at your picture or have no idea what you are doing so feel free to ignore them.

Question 1: what's in your .xinitrc?

Question 2: why are you starting X this way? It's not for beginners, and from your question it doesn't sound like you're an advanced user.

How did you go about installing the other two packages from git? Do you know what directory they were first cloned to? Did you build from source or run an executable like an appimage? Did any of these actions occur prior to the install of masterpdfeditor?

https://forum.endeavouros.com/t/graphical-session-doesnt-start-first-time-invalid-mit-magic-cookie-1/5947/8

Check /etc/hostname

This 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.