Resisting sleep with help can be a sign he's ready to try self-settling. I'd try putting him down awake and see what happens. Maybe comfort him in his cot if he gets annoyed. Singing has worked well for my babies. Mini nap routine white noise dark room, about 15 minutes before nap is due.
I am in the same boat with regards to my baby resisting his day time naps! Not much help but am right here with you!
It's happening to me too It's supposed to be a sign they are ready to step away from contact naps and nap independently but like you my little one won't nap elsewhere during the day , at this age we're supposed to be working on crib napping for his first nap of the day when hes melatonin is still relatively high, I've been doing it the last 2 weeks and it's really tough doesn't seem like I'm getting anywhere Sorry I'm not much help but this was the advice given to me by a sleep consultant