4 players or more
Why am I not able to play with 4 players or more?
My friends and I made sure to buy the base game but we aren’t able to play more than 3 for some reason
Four players is the maximum. I don't think you can play more than three people in a custom match unless the person hosting owns the game/expansion you are trying to play. Then (I think) you can play four people, but it might be that all four need to have the game/expansion you want to play.
@LemuelB2 I can confirm that all players need to own the expansion.
And 4 is the max number of players on Catan Universe so far.
If you want to play with more players, you can buy the board game (analog, I mean).