PlayerControllers exist only on server and client that PlayerController belongs to (if there 2 local players there wll be 2 PCs, so all local players), other players clients can’t access PlayerControllers of other players, they simply don’t exist on them. If you want to share some data to other players you place it in PlayerState which is replicated to all clients.
Just hands up, same goes with GameMode, but it only exist on server and same as with PC there GameState class to shere data with clients
This is all for security reasons