Well, in terms of online, I think it is hard to do unless you are on a Discord call or something. I'm not much of a poker player, but what is the benefit of having collusion? Most likely, it is to gang up on one player? I mean, that's just really unfair.
I don't think any technology right now is capable of detecting that because there are different connections to a game, maybe just randomized to joining of games or something.
Even in a Discord call or a Video group, it can still be done. All they need is another messaging app to do the trick.
Truly, this is unethical, and all we can do is make sure that every player doesn't know each other. It's tough to do that, especially if these people are targeting players and would just fake their connection to each other.
Well, if we are doubting, it's best if we just go to a physical poker room and play there. Face-to-face, they won't be able to do that without someone noticing it.