@art have you installed the firmware package? firmware-amd-graphics
@art watch out for which PCIe Slots you use for your gfx card. if there are two, only one may be powered via the card edge connector. the other might require external (separat cable) power to your gfx card.
"I appreciate SDF but it's a general-purpose server and the name doesn't make it obvious that it's about art." - Eugen Rochko