Description of feature
Right now, there is no way to make a wither storm move other then survival player (and command obviously)

The thing is, if I wanna try out and also see how it moves and stuff, but don't want to get caught in a beam every 2 second, I can't, since there is no way to make a wither storm follow a player that is in creative or spectator

Yes it does follow creative players. In the recent 1.18 update you can set the WS ultimate target to a specific player, info on how in the “For creative users” spoiler on the mod page

Yeah I am dumb, I just didn't realised that it slows down a lot after it caught you for the first time and though it just didn't move at all

It should still follow in Creative, it did with me.