No blur in gnome lock screen - bad graphics configuration?

Please help me pinpoint the cause of the horrible gnome lock image.
The GNOME lock image should look pretty blurry. In my case, it resembles a gradient structure.
There is also a shadow problem under the nautilus window (no blur). Especially visible against a black background.
I have no idea where to look for the cause. Any help is appreciated.

Lenovo ThinkPad L14
AMD Ryzen 7
GPU: AMD VEGA 7 Renoir
Fedora 33 Workstation (kernel 5.9.16)