Guides
Does Graveyard Keeper 2 Have Multiplayer?
The current official play-mode listing, without speculation.
Current official listing
The Steam feature list and the Lazy Bear Games page currently list Graveyard Keeper 2 as single-player.
What that does not prove
This is a description of current official listings, not a prediction about every future update. No unsupported claim is made about whether another mode could ever be announced.