Is Graveyard Keeper 2 multiplayer?
No. Graveyard Keeper 2 is single-player only. The Steam store page lists no co-op, no online multiplayer and no multiplayer tags of any kind — and neither the announcement trailer nor any of the official write-ups mention playing with friends. The first game was single-player too, so this isn't a surprise.
What the store page actually lists
Steam's feature list for Graveyard Keeper 2 is: single-player, full controller support, Steam Input, DualShock and DualSense support, and Family Sharing. Notice what isn't there — no "multi-player", no "co-op", no "online PvP". Those are separate tags Steam shows when they exist, and none of them are on this page.
For the console versions (PS5, Switch, Xbox Series), nothing in the official announcements suggests multiplayer either. Same game, same design. If you were hoping to dig graves with a friend, this isn't that game.
Wait, but zombies?
The undead army in the trailers is your workforce — an automation system, not a multiplayer feature. You command them, they do the hauling and the fighting. Think of them as very motivated employees, not as other players.