I'm not going to write a bug report as I have too little info to justify it, but I figured a thread is in order. If you know of any bugs that match this description, please let me know so I can monitor them for a solution.

Earlier today, a Plasma desktop crash was able to render my system unusable even after a system restart. Whenever I attempted to start the desktop, the "plasmashell" process would freeze and the desktop stayed black... upon inspecting the process in Ksysguard, you would see its CPU status saying "stopped". It appears that upon crashing, Plasma corrupted something in the cache directory (~./cache): The issue was only resolved after I logged in as root, and deleted most of the contents of the .cache folder... which apparently had to include items that were last modified long before the crash.

I decided to post in order to let you know there is an issue that can permanently break the desktop. If you experience something similar, you must delete your "~/.cache" to get the system working again. I lost an hour figuring out how to repair it, and I hope this can be found and fixed so other users won't have to experience the same thing.

Hi!

I am experiencing this right now.
I followed your advice and ran $ rm -rf ~/.cache/*
but it didn't help.
My desktop is still black

I am a super newbie and have no clue what to do next.
Do you have any advice/ idea/ solution?

Thank you very much!!

Oh and i'm using
Antergos with linux-macbook kernel.

THX

The issue was caused by a broken version of MESA, it was fixed a few weeks after I reported it. You need to delete both "/var/lib/sddm/.cache" and "/home/user/.cache/qtshadercache" to fix the system if you had the broken library.