Depends on many things.

But ideally you want some game logic on the server side, to prevent cheating.

You can just sync world state between players, but that will always cause weird glitches.

I don’t develop games, so I’m no expert, but I my backend would have the ‘one true’ state of the world, and players would only interact with it by using verified actions.

I did one such game, but it was turn-based tabletop, not very comparable to open-world games.