Lines render at the corners of the sky when FOV is specifically 90 and when the rotation is set to specific values (Can be closed as a Duplicate of MC-220195).

Note: I'm playing with absolutely no modifications, pure vanilla Minecraft, no data packs, no resource packs, and no mods, and in singleplayer. In my survival world ever since I updated to 1.17, whenever I slept in a bed I noticed something weird where there were strange white lines rendering at the corner of the sky. When I got out of bed the lines didn't vanish, but as soon as I moved my rotation, they vanished. It eventually annoyed me so much I tested this in another world and found the same result, But then I realized it is because the bed sets me at rotation of 0 0. And I was right because with commands to be set at rotation 0 0, the lines appeared, but when I rotated they disappeared. I like to have my FOV higher than normal at 90, and when I adjusted my FOV to any other number I noticed the lines didn't appear at 0 0 rotation. After many many FOV adjustments I have to conclude this only happens with FOV at 90. But if you find these lines at another FOV setting please comment. I tested this in 1.16.5 and found this didn't happen, so this is a new bug from 1.17. I've searched very hard and found nothing such like this. If more information is needed please tell me, but to sum it up, to reproduce, create or join a world in 1.17 or 1.17.1 Pre-release 1, set the FOV to 90, make sure cheats are on, then run the command: /tp @p ~ ~ ~ 0 0, alternatively, instead of running the command you can sleep in a bed and get the same result, when one of these two things are done, notice the white lines in the corner of the sky. Also, I just realized this also happens with rotation as 45 0, 90 0, 135 0, 180 0, 225 0, 270 0, and 315 0. Notice how the bug occurs every exact 45 degrees of rotation.