I don’t know how exactly, but I had working suspend functionality on my laptop for the last few months using the open source Nouveau driver. But since that now caused other problems (see Okular and Kate slow ~5 second start ) I re-installed the proprietary NVIDIA drivers. That solved the other problem, but after forgetting to unmount an sshfs directory and the laptop trying to go to sleep I had to kill him with the REISUB method since no matter what else I tried it didn’t sleep, didn’t wake up, and just showed me a frozen non-blinking cursor underline symbol in the top left corner of my screen.
I tested the suspend manually before that after installing the proprietary NVIDIA after rebooting to use them - but without having an sshfs mount active and it worked just fine.