I was thinking it would work like the Act 2 battles on the console versions of Inscryption. Its very simple with basically just selecting a card and pressing A. I have a couple clips of the switch version card battling in Act 2 I could send you on discord for reference, if you'd like. :3
Yeah, just send on discord @femb0yash if you can :3
(Sorry for taking so long to respond, for some reason itch decided to mark your comment as spam and hide it :/)
Edit: couple days ago they sent me the clips, I also managed to obtain totally-not-pirated copy of Inscryption for Switch, and controller support will actually be included (to the best of our abilities) in the 2.0 update on all platforms! (But I must say, some platforms/gamepads do some rather silly shit related to mapping buttons, and we're not yet sure we have universal solution for that)