I read the link that was referenced in this post. The final post was made by a member who is rarely online, but is a vet, so her diagnosis is probably accurate.
Since the skin looks fine and there appears to be no mange or mites, I think this could be helped with proper nutrition.
The baby looks young enough to still be on formula. Are you providing formula? If so which one?
This baby needs time to regrow her fur and based on where you’re located releasing this winter would be a death sentence. It will need to be overwintered. Are you in a position to keep him until next spring?
A good quality squirrel block should be purchased. Go to Henry’s Pets online and order a bag of Picky Eater blocks. This will be a great way to provide proper nutrition when combined with some healthy veggies/fruits. Here’s the healthy diet for captive squirrels.
https://thesquirrelboard.com/forums/...-Pet-Squirrels
Before placing the order, please verify about the formula because Henrys also sells the appropriate squirrel formula needed which is Fox Valley 20/50.