You can change BIOS on your Vega 56/64 card with a DIP switch on top of the card, near the PCIe bracket.

There are two different BIOS versions (both will show normal grey boot screen and boot picker):

- standard BIOS for Apple Mac Pro (recommended for macOS Big Sur/Monterey/Ventura/Sonoma/Sequoia) with all display outputs working, and minimal fan noise when idle, also GPU Tach activity LEDs are enabled

- special BIOS version for Mac Pro (recommended for macOS High Sierra/Mojave/Catalina) with lowest DisplayPort output disabled and zero fan noise when idle (with the exception of macOS High Sierra), also GPU Tach activity LEDs are disabled