I tried this but for some reason the AMD software doest recognise (in Windows 10 running Parallels) that I have an AMD video card at all - even though clearly I do.
Using a 2020 iMac 27" (AMD Radeon Pro 5700)
iMac 27″, macOS 10.15
virtual machines does not have on the metal gpu they use a virtual machine generic gpu driver, you can't access your video card special features or play fancy 3d games in virtual machines.
If you install Windows using Bootcamp, then you can Update AMD graphics drivers for Windows in Boot Camp - Apple Support. Check Windows Device Manager -> Display Adapter for the current driver in use.
How can I update a graphics driver in Parallels?
