DISCLAIMER: I am not sure if this is a bug. But blocks in game, past a certain distance(two chunks or so, I believe), show their outline, as if they were selected. I have not tested very many versions, but it appears to affect all installations so far(1.16, 1.12.2). Unfortunately, I have no other computers to replicate this on, and am unable to determine if this is an in-game rendering error, or an error with my PC, or anything else. The glitch is especially apparent on superflat worlds, where flying up reveals a moiré pattern of outlines. It also appears to affect clouds, though not as noticeably.
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The curved lines in the second screenshot is MC-234358 (Moiré pattern), and for the first screenshot with the rendering issues, that's caused by either outdated graphics drivers, or using a modified version of the game.

the game isn't modified... I'll check the drivers, but as far as I know, it was working fine until now. I'll see if it happens on multiple computers as well, but yes, the graphics drivers are my suspicion.

MC-234358 does seem to have the same viewing distance as I do, but that only happens with certain blocks, not all of them. with this, it happens with all of the blocks beyond about 16 meters away.
Thank you for your report!
We're tracking this issue in MC-1794, so this ticket is being resolved and linked as a duplicate.
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Ok, can confirm that this was not a bug and that I was just being dumb with the NVIDIA control panel settings.