The card being Nvidia or AMD doesn't mean squat here.
Those tabs fit in beside the board. There are usually some slots along the edge of the motherboard tray of your case that they slide into. Verify that you are trying to use the correct PCIE slot on your board, usually the top full sized one. Make sure that you aren't snagging them in the slots in the back of the case (guilty of that myself many times over). The pic shows the gap along the rear of the mobo where those tabs go.