First Look at the "Spectator Mode" for Mobile version
https://x.com/AnakinJuegos/status/1925820776378212533
they have a built in UI that is similar to tournament UIs right in the game that it details player's economy, ultimate points and their status.
Unlike PC it would be just blank screen with no player bars on the side (and the tournament UI had to be requested or pay to Riot to use it)
Additionally, Custom lobbies in Mobile is now a server browser like Dota2 where you can browse rooms to join