AMD's new RX 9000 GPUs only officially support UEFI systems
by from Latest from Tom's Hardware on (#6VNYG)
Radeon RX 9000 series GPUs will require UEFI for optimal performance and may not work as expected on older CSM/Legacy Modes.Radeon RX 9000 series GPUs will require UEFI for optimal performance and may not work as expected on older CSM/Legacy Modes.