Display shows flicker effect — GPU, Logic Board, or software issue?

My Macbook Pro 13” early 2015 shows a really strange glitch or flicker problem since a few days. The issue first started appearing a few days ago after using the built in screen recording tool of macOS. It seems to intensify under heavy use. See attached video and photos. What I have tried so far to fix it:

• reset NVRAM + SMC; the issue persists
• safe mode (reboot + shift); here I wasn’t able to reproduce the issue
• Apple diagnostics (reboot + D); didn’t report any errors
• Apple recovery (reboot + R); here the issue does not show up either
• reinstalling macOS via recovery (not clean install!); after doing so the issue persists
• hooking Macbook up to external display; the issue also shows up there (which makes me conclude it the issue is not caused by my internal display)
• uninstalling all unnecessary software + removing login items; no difference
• activate color filters via accessibility, activate different color profiles in display preferences (found these tips online); no difference
• creating new empty user; the issue was also appearing there (even on the login screen it shows up occasionally, but never in the boot screen with the Apple logo and white progress bar)
• interestingly, the issue shows up in screenshots (see attached)
• even more interestingly, the flicker seems to affect everything BUT the cursor; when I move it through areas that are flickering it moves OVER them without being affected

What I see as possible causes: software issue, GPU or something Logic Board related. Though the cursor not being affected speaks against a hardware problem in my understanding. My last ideas are to upgrade to Monterey (currently I am on Big Sur) and, if that doesn’t show a difference, wipe the whole machine and do a clean install of Monterey from a stick. Other than that I am out of ideas. If anyone has any tips that would be really helpful.

My setup:

• Macbook Pro 13 inch early 2015
• Intel i7 3,1 Ghz
• Intel Iris Graphics 6100 (note: no dual GPU since 13 inch model)
• 8GB RAM
• 512GB SSD