Most wheel covers look nice. That's all.
You might cut some thin plywood to the size of the tire .. Trim the edge so it does not tear up the wheel cover. and put that behind the cover.
WHY do they "look nice" but that's about all. UV light is what damages the tire and it goes straight through the cover like it was not even thre in all too many cases.
I thin they do make some that claim to block UV but I've never seen
Tries. Best way to protect 'em.. Well DRIVE from time to time Worst thing for tires is Parked.