Inappropriate self touching - get child to stop

My son who’s almost 10 is adhd and autistic level 1 or 2 (diagnosed 2 but closer to 1) He is always putting his hands in his underwear, and is doing it absentmindedly. I need it to stop.

I’m trying different underwear but no success yet. (If you have a kind you recommend, please share in case this is mostly sensory!). He had no medical issues there. I’ve tried commando but doesn’t stop. He’s verbal and says it doesn’t hurt or itch or anything. Underwear does irritate him but he’ll keep doing it when naked too.

Any other suggestions??

Edit to add: it does not appear to be masturbation, it happens all the time in public as well, and it’s touching his privates, not just inside of clothing.

Based on comments, I’m thinking it’s a form of stimming as he does it mindlessly so I will try getting him some fidget toys to carry around in pockets, and maybe a belt with things attached to play with.

Thank you for comments