Ok everyone, I have great news ! (edit: not so great)
I managed to fix the issue (edit: nope).
Just as I suspected, it is indeed a power management issue where the panel tries to optimize power consumption by utilizing a technology called "panel self-refresh" which basically allows the screen electronics to refresh its current image independent of the graphics card if nothing has changed on the screen. You must disable that.
Here are the steps:
- Open Microsoft Store, then search for and install "Intel® Graphics Command Center".
- Open the app, go the "System" vertical tab, then go the "Power" horizontal tab
- Disable the "Panel Self-Refresh" option on both "On Battery" and "Plugged In" modes.
The problem should instantly disappear, even before you leave the app.
EDIT: Unfortunately, the problem will only lessen in frequency, but will not disappear completely. But I will leave this post here, maybe it helps in some cases.