i mean the /debug report command, it is replaced with F3+L and /perf (check the wiki page about the debug command https://minecraft.fandom.com/wiki/Commands/debug)
this was removed in 1.17 prerelease 1
i think you're experiencing a moire pattern: https://en.wikipedia.org/wiki/Moir%C3%A9_pattern
they're mostly unavoidable if you have lots of blocks with fine lines on them (like stone bricks) and view them from a distance
works as intended (i suggest you look at the snapshot page for 20w49a)
can confirm
What's a cracked launcher?
in the minecraft wiki, it says that this is caused by a discrepancy between an enderman's eyes and body textures. The texture for their eyes is located at a different texture file than the body, which is what allows the eyes to glow. However, this also means that they don't perfectly line up, so forcing an enderman to look up will render its eyes completely white.