The screen blinks black when the frames go down to 1 FPS because im sharing the window to Discord, maybe you can fix it, maybe not ;)
(Using version 2.1)
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#49 sorry for duplicate didn't search before posting

I've located the issue to only appear when using optifine & optifabric

Nice work tracking it down! Too bad it's OptiFine… my stance on OptiFine is that its closed-source nature makes it all-but-impossible to support, and there are much better alternatives out there for most of its features these days.

Yeah its a bummer Optifine is closed down, will look into the alternatives, thanks!