Can't join my own server that I'm hosting on my computer

Facing commands don't work how they should

Effects use the whole "gui.png" picture, and not the image inside the picture.

Get "No targets matched selector" when try to use /kill command

In realms, when I drop a block on the ground it lags a lot and looks very choppy

When I type in a command block sometimes the command won't save and I have to retype it.

When I type the command to give me an item in a certain slot, it lags my inventory

when I tried to type a command into a command block it turned into a bunch of #

I purchased realms + and I cant replace the default world with my other world, plz help