It isn't a 1.17.1 bug you dumb bot :/
This website is for vanilla Minecraft bug reports. If you have any problems with a mod, contact the mod creator.
For feature requests, go here: https://feedback.minecraft.net/hc/en-us
Also, if you look at your inventory while flying straight down with an elytra the player character takes up like half of the inventory space but it is kind of cool. It probably is intended though.
This website is for reporting bugs. For your suggestions about Minecraft you can go here https://feedback.minecraft.net/hc/en-us
Have you got the same mods? Because you need to have them to join another modded world.
Is your problem that many people can't play in a server with the same account? Because that's absolutely intended and it would be illogical to let it happen.
A zombie in my iron farm became invisible ( also he was wearing armor) and then I was nearly killed by a ton of invisible drowned. Also, when I was raiding a bastion, I lost all my stuff because of invisible and immortal piglin brutes.
I can add that in the nether biomes not only do they look like the overworld they also have hoglins and piglins turning into the zombified versions.