It sounds like you're looking for the (Nintendo Switch game package) and update files for Persona 4 Arena Ultimax on a modded/hacked Switch (using custom firmware like Atmosphere).
: Note that unlike the PC and PS4 versions, the Switch version does support rollback netcode and uses delay-based netcode. : The full game installation on Switch is approximately Key Features Dual Story Campaigns : Features the complete story modes from both the original Persona 4 Arena Shadow Types persona 4 arena ultimax switch nsp update hot