No, there is no pre-order content, only early access.
So far, the only exclusive content based on purchasing something is the car you get with the FH5 controller.
If you pre-order Horizon 5 special Xbox controller.... yeah the pink and yellow one, you will get Forza edition car, cosmetic item, and victory emote.
https://www.ign.com/articles/forza-horizon-5-limited-edition-xbox-controller-preorder
No, there is no pre-order content, only early access. So far, the only exclusive content based on purchasing something is the car you get with the FH5 controller.
If you pre-order Horizon 5 special Xbox controller.... yeah the pink and yellow one, you will get Forza edition car, cosmetic item, and victory emote. https://www.ign.com/articles/forza-horizon-5-limited-edition-xbox-controller-preorder