Any tips on how to get baby to nap longer and go down better during the day?

My little guy will be 6 months on Monday and I'm lucky if he sleeps longer than 30 minutes for his nap. I really feel he needs longer naps at this point but don't know how to help facilitate that. He often wakes up fussy and still acting tired but I can't get him back to sleep. He naps almost every 2 hours (if I can get him down, he fights it even though he's clearly tired) and usually has 3-4 naps a day. Bedtime at 7.

He sleeps 11-12 hours at night with one night waking/feeding most nights. Of note he used to sleep 11+ hours at night without waking.

He is teething. We recently started solids. We recently transitioned him into his crib and room at night although he's been napping there for a couple of months.

We do white noise, shades drawn, a swaddle and a diaper change before nap. A routine he's familiar with.

He sucks his thumb but used to be better at soothing himself than he is now. Not sure why this changed.

Any advice is appreciated.