All variants together

Combining any variants other than 960's is pointless

And how should a game work then? Every variant has its own rules.

You combine those rules.
For example, antichess and atomic put together.
Rules: lose to win. Any piece you capture will make your piece, your opponents piece, and the pieces around it.

You can’t check in RK so how do you win in 3+

RK, Chess960 and From Position don’t start regularly so it wouldn’t work for the others.

Even if there is a variant that combines all of the other variants, don't you think it will be very hectic and confusing?

Besides the valid point that some combinations are not really possible or do not make sense, several of the possible hybrid variants also are seriously flawed, e.g., crazyhouse+3check, crazyhouse+atomic, and atomic+anti+KotH all have been shown to be a forced win for white in <= 20 moves. So simply mixing together several variants does not necessarily result in an interesting game.

Combing some of the rules of all the variants might work.

Some variants do not work together