Check if there are problems with Optifine installed. I saw several videos where the own hat model is not rendered. Maybe this has something to do with Optifine.

Nope, there is no general problem with Optifine.

Very thoughtful issue management.

By the way, it is possible that hat rendering can be disabled by players if they wear hats in Curios slots, since Curios itself provides such feature. You probably know already, but just in case.

hehe thanks ^^

Yes, disabling hat rendering is possible when worn in a curios slot :)