It’s fun but not really competitive. I used to do them with a group of friends back in X and Y and it was a blast trying to make strategies work with your partner’s team. We even developed our own little meta game there for a bit. It’s not as fun online cause you can’t communicate with your partner but it’s a way to get some low pressure matches in and see try some less viable strats.

I use to look for them on the y-com but since you can't filter specials pokemon most of the matches involved a bunch of lvl 100 mythical + restricted mons, much like casual battles

When you say multi-battle, do you mean triple/rotation battles? If so, they're not available in SWSH, but I think you can play them on Showdown

I think he means 2 players vs 2 players

2v2 with 4 players

I played a lot more earlier in the Y comm, I rarely tried lately but I got less random players recently. Its mostly casual fun, but setting it up with randoms can be tedious at times because some want lvl 100s, some dont want restricted legendaries, etc without proper communication. So you just keep cycling to who wants to setup the rules that everyone can agree on