Split screen. It working on X Box one. It seems the start button which it says to use to get second person to sign in does nothing. The controller seems to work controlling everything else so it is synced. I haven’t seen any good responses to this which is surprising as there are quite a few posts about it.
I remember playing a split screen session a few months back on the Xbox One.
Have you tried to sign in the second controller as a “guest”. This is usually required by many local multiplayer games (for example Overcooked). Here’s a guide: Xbox Support