Implementing multiplayer is hard. Really hard. It usually is far beyond the capabilities of the usual indie developer releasing their project on Itch and Itch alone.
Also Itch has no support for playing with other Itch users.
So the typical Itch user is not used to multiplayer games and is not seeking them here. 2% of the games are tagged multiplayer here. On Steam it is 10%.
What I am trying to say, you need to market it elsewhere and not by existing on Itch alone. Itch will not promote it for you the way Steam would. There is a tiny recommended section, but it is mostly overlooked and underused in my opinion.
Which brings you to the basic problem of how to market a game when no one knows you and you probably have no budget. There are many threads about this.