Honzall, many thanks for this. For anyone else with a 27" Mac and stuck with a low res screen display in Big Sur, this certainly works. I originally hit this bug when I installed macOS 11.01. Thinking it may have been bugged, I scrapped it and waited till 11.1 was released. It installed fine first time but when 11.2 was released and I decided to install it as a VM, I was back to staring at a low res screen with Graphics again set to 3Mb, despite allocating 512Mb in configuration. Reinstalling Parallels Tools didn't help either so I'd almost decided to write off my 11.2 VM when I read the above. Thanks once again.