@futurecop
Update:
Lowering the UI resolution down to 720p seems to have done the trick, the glitch appears very rarely now.

I guess you can lock the thread now.

POSSIBLE SOLUTION!

UI Resolution in Settings->System->Display, set it to 720, which I could have sworn I had done before.
This makes the glitch appear only once in a blue moon, most likely to happen while switching from Recalbox to KODI.
I've also "Set GUI resolution limit" in the same sub-menu to 1080/720 (>30Hz), perhaps that'll lock it in place and guarantee its stability.

@alvin
Thanks for the input. Yes, I would very much like to keep the all-in-one multimedia entertainment center I have set up right now.
I've used LibreElec a couple of years ago when I was still very new to this, but using the RaspiOS gives me access to streaming websites as well as jolly file sharing.
I've asked the same question in the KODI support forums and will report any successful solutions I might find.

@zing
Nope, didn't help.

@zing
Yes and yes. I've changed video resolutions, UI resolutions (which improved menu navigation speed a little, but didn't fix the original problem), framerate settings, rendering modes (one of which crashes Kodi with no survivors), HOWEVER:
all of the above was changed within Kodi interface, I've never really fiddled with Recalbox config file. I'll try that later, thanks!

First off, this is the project I've been dreaming about, having everything nice and accessible from one point and turning my dumbass TV into a SMART TV. Great job!
However there is one issue that keeps bugging me: The static artifact. It does not occur on any other Kodi installation. I've searched high and low on all the forums and search engines for a solution since I know you guys are focused more on the emulator part.
During playback (and occasionally in the UI itself while no video is playing) 5%-20% of the bottom of the screen turns into static for a few milliseconds. Some movies are more prone to this behavior than others (despite sharing the exact same resolution and format as others) and like I said, it sometimes happens while simply browsing the menus. It's not tied to specific files or timecodes, but it seems to be sensitive to skipping forward and back. Sometimes it would happen only a couple of times throughout the whole movie, sometimes it's 10 glitches back to back in a span of a minute.

Here's an example (filmed at 30fps the glitch appears for 2 frames):

And another one:
https://i.postimg.cc/cL65yh2H/5.jpg
https://i.postimg.cc/fRFqwXQv/6.jpg
https://i.postimg.cc/3wvSW-RKQ/7.jpg
https://i.postimg.cc/ZRzfNSRB/8.jpg

Link to both examples:
https://postimg.cc/gallery/xSbzTbg

Thanks in advance and god speed!