This page of the guide to LEGO Star Wars: The Skywalker Saga explains whether the game features multiplayer or split-screen co-op.
Split screen co-op
LEGO Star Wars: The Skywalker Saga features split-screen co-op. In order to play together you must connect a second controller and log in to a different account. The game will automatically split the screen and the other player can immediately jump in.
Player two can leave the game at any time by disconnecting their controller. This makes the game go back to singleplayer. Co-op only supports two people at once.
Just like in the previous games in the series, LEGO Star Wars: The Skywalker Saga doesn't contain multiplayer.