i found out how to """prevent""" miis from teleporting
as far as ive seen it only works for about 3-4 minutes or so AND you need to keep an eye on them (like physically keep them in your line of sight) so that they dont teleport. So its mainly just a monitored timeout instead of actually banishing them sorry for the clickbait title
but literally the only thing you need is a vending machine. Just one. You don't even need walls. After they interact with the machine they enter this almost trance like state where they won't try to teleport back for about 3.5 or so minutes, any sort of floor tiles and not giving them gifts or anything of the sort also works as they'll just roam around regardless
there's probably way better methods of doing this but i genuinely haven't seen anyone bring this up and the other method is to bring their house along which is preeetty ugly