I noticed that one tire had the cracks too. Both of my front tires, look like that and have been since last year. Wasn't until coming back from the Haspin Rally I noticed one had two big gashes in the sidewall that make me nervous so when I get time, I have two decent Goodyear's to swap them out with.
I use this tire conditioner and it seems to be some good stuff, makes the tires look new while providing some protection from the UV rays. Be good to use on the good tires to help them last longer.
Tire Dressing, Tire Protectant, No Tire Shine, No Dirt Attracting Residue 32oz Natural Satin/Matte Finish, Aircraft Grade Rubber Tire Care Conditioner, Better Than Automotive Products
https://a.co/d/fHeIJd0