I was trying to name my pet Allay "Allay" and minecraft censored it, at first I believed this to be intentional until I tried naming it literally anything else. I tried the following
Tim
32 A
Hello
I even ended up trying basic words like block names in minecraft and everything would censor no matter what I would type rendering the nametag useless. I am on a realm and have not tried to do this on a single player world yet so Im not sure if its just specific to realms.