When you use retroarch, players 9 and 10 do not work. 8 controllers seems to be the maximum number that retroarch will accept at one time. I do not think this issue has been well documented because Saturn Bomberman is the only game on retroarch that I am aware of that supports up to ten controllers simultaneously. One redditor says the issue also applies to players 11-16 as well, but I do not have any 16 player games to test that theory out on: https://www.reddit.com/r/RetroArch/comments/xurnwi/anyone_else_unable_to_use_more_than_8_controllers/
Before anyone asks, I have gone to Core Options
> Input
> and set 6Player Adaptor on Port 1
and 6Player Adaptor on Port 2
to ON
. I have also gone to Settings > Input > Maximum Users
and tried 10, 12, and 16 players, but nothing worked.
I am currently trying to get this working on the steam deck. supports 10+ controllers at the same time (I have tested ten simultaneous controller on 10 player PICO Park: Classic Edition, and it works great).
It does not appear that anyone has been able to get 10 players simultaneous play working on RetroArch: https://www.reddit.com/r/RetroArch/comments/yvhkk8/10_players_saturn_bomberman_on_the_steam_deck/