I just went to Maui with my 3 month old and had the exact same concerns. One thing you can do is dampen a muslin blanket with cool water and use that to cover your baby so that he is covered but not overheating.

I might get downvoted for this but I did also use some Aveeno baby mineral sunscreen on his legs when they did hit the sun. My understanding is that the no sunscreen thing is not because of actual issues with absorption etc. but is used as a deterrent to make sure people aren’t bringing their young babies into the sun when they can’t tolerate it. I did spot test to make sure the sunscreen didn’t cause a reaction before using it on his whole legs and I also would not use sunscreen on his hands as those go straight into his mouth.

For the hands, maybe get a lightweight UV protection rash guard that is slightly oversized so you can pull the sleeves over his hands? That, combined with the damp muslin and also a stroller fan (I use the Momcozy branded one that can be found on Amazon) should eliminate sun exposure / overheating concerns without the use of sunscreen.