I’m very concerned, the skin doesn’t look irritated so hopefully that’s a good thing. Please let me know if you’ve seen this before, I’ve googled and such but there’s a lot of possibilities.
According to my thinking, this is a bacterial skin infection specifically known as the staph infection caused by staphylococcus aureus (bacteria). It usually doesn't cause irritation, itching, or swelling. But in severe cases may cause redness, inflammation, and bald spots on the skin.
I think visiting a veterinarian clinic would be a great idea.
The Safest quick test is to treat it as Feline acne and cleanse it gently with a few drops of iodine solution diluted in a cup of warm water (iced tea colored -- it will sting your kitty if it's not extremely diluted.) Also clean his back and front claws with the same solution since he will be scratching with dirty claws and reintroducing germs. Only a quick pat with a dripping wet napkin is necessary.
He will probably struggle when he feels the sting or if the water is cold so hold him fast and play with him afterward to make him forgive you. It also helps to approach him from behind like you're going to pet him. No cat reacts well to foreign objects coming toward their face in my experience. Source I have a cat with sensitive skin, and also allergies that cause terrible open acne wounds on her chin and face. This method has always worked on her.
If this has no effect in a few days you need a vet.
The spot seems to be in the ideal location to be scratched regularly by his back claws so I would bet that it is irritating him even if it's not Feline Acne. The wet napkin should also be helpful removing any irritants that got rubbed on him.