There are no Win.8.1 drivers for any newer amd cards.
AMD stopped support for the OS in July 2017.
Some say the Win7 drivers work ?, or move to Win10.
My PC- Ryzen 5 5600x, B550 aorus pro ac, Hyper 212 black, 2 x 16gb F4-3600c16dgtzn kit, NM790 2TB, Nitro+RX6900XT, RM850, Win.10 Pro., LC27G55T.