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.
I agree with your statement.
I mean hypothetically speaking, there is that possibility of collusion but I highly doubt that it happens in this kind of setting. Additionally, this can also happen specifically in some games where there is skill involved (e.g. poker) where players get to participate in one field. The only problem is, some gambling websites have devised a way in order to prevent this from happening- you join random rooms instead of participating and choosing your desired room.
There was this time someone complained that he and his friend connived to cheat another poker player by making him lose only for his friend to cheat him in the end to win the game.
My conclusion on cheating in poker game is that, one day the one who thinks he can cheat very well will get in a position where if he does, it will affect him and he will found someone who can cheat him too.
That may be true but I really doubt that collusion may happen in gambling. I mean, there are lots of factors to consider and with all the possibilities in gambling, it's near impossible to do it successfully.