[NV50, Linux 5.9] Regression: Visual artifacts and eventual GPU crash

With my Geforce GTX 285 04:00.0 VGA compatible controller: NVIDIA Corporation GT200b [GeForce GTX 285] (rev a1)

I experience a regression after updating to Linux 5.9 from Linux 5.8.14 where visual artifacts appear on the screen after a few minutes, leading a lockup of my display, forcing me to reboot the PC. Downgrading fixes the issue again.

Other software versions: X: 1.20.9 Mesa 20.2.0 KDE Plasma 5.20.0 (kwin)

The journalctl contains the following errors:

Oct 14 16:46:17 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
Oct 14 16:46:19 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
Oct 14 16:46:21 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
Oct 14 16:46:23 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
Oct 14 16:46:25 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
(repeats)
...issue command to shut down here...
Oct 14 16:48:18 bastian-desktop kernel: nouveau 0000:04:00.0: DRM: base-0: timeout
Oct 14 16:48:18 bastian-desktop kernel: nouveau 0000:04:00.0: disp: ERROR 5 [INVALID_STATE] 0b [] chid 1 mthd 0080 data 00000001

I already tried to run a bisect, but it wasn't conclusive since I think I made mistakes when tagging versions good or bad, since it some times takes a while for the issue to manifest itself. The first commit that had errors in the journal was 5de5b6ec but there probably were bad commits before which I didn't tag correctly.