What fixed it for me:
Step 1: Uninstalling GPU Drivers and Radeon Suite with Display Driver Uninstaller
Step 2: Installing the older Win10-radeon-software-adrenalin-2020-edition-20.10.1-oct19
Newest Radeon Pro and Enterprise Drivers hinder Material Preview & Eevee Rendering in Blender. (Grey Objects, Textures and Shapes not displayed correctly)
Pretty sure it's the same or similar issue:
Tested different Blender Versions from 2.8 Final Releases to 2.92 Alpha.
Running Win10 64 and a R9 280x Vega.
If I can provide further information to help you fix this issue, please contact me.
Thank you very much for your support.
Sounds funny, when we AMD released a driver for the same type of VGA, but a driver version is available for content creators or some sort of regular driver.
Amd vga users like me are confused. Not to mention my problem with Radeon Prorender, no one has answered yet.