Installed bazzite on my fiance's PC, this is now happening a week in, no new apps or installs
(sh.itjust.works)
If you installed the NVIDIA proprietary drivers, you should have the nvidia-settings (GUI) and nvidia-smi (command line) tools installed already. They should be able to tell you the GPU temperature, fan speed, etc.
Edit: At least, that's been the case on all the Linux systems I've had NVIDIA proprietary drivers on in the past.