Same as Amy I'd say dark room, white noise, and check you are on the right wake windows for Lo's age.
no real advice sorry other than they may just not need it! my first only napped for 20mins at a time until he dropped to one nap and that was then 45min-1 hour. Always seemed sufficient for him, however frustrating I found it! some babies just need less sleep than others - feels unfair when people have babies who nap for 2+ hours 😅
Are you building up enough sleep pressure? Is the room dark? White noise? X