Is that the last page from the journactl output after you play a game? Did you press “End” key after executing journalctl command?
I don’t really understand technically, I’m not technician so I might be wrong, but looks like your CPU cores went to a sleep mode in a middle of doing something. Your CPU lost power. Hmm, Isn’t that kinda odd? Or is it a feature?
I’m still suspecting this is a firmware issue related to power management but can you try different kernel. Use LTS kernel 5.4.
PS:
Quickly after BIOS boot press Esc to show Manjaro GRUB and choose kernel 5.4 (after you install it). The GRUB might not show up if you don’t do that and automatically select the latest kernel available.
Edit:
Oh, I forgot something. When your laptop is laggy, please execute cpupower frequency-info and post the output. I’ve found some info about gnome being sluggish after waking up from sleep mode.
Edit again:
While checking cpupower, please open nvidia xserver setting, quickly go to power mizer and make sure it show that your gpu performance is at max level before going down. Just to make sure it’s not gpu fault.
Another Edit:
This post might be related: Issues with mouse stutter
The OP use LTS kernel, but I suggest you still try it as there is a chance that these are different issues. I hope Manjaro devs take notice of these reports.