Sounds like you have one of 5900 with disabled 2nd chip (there are web articles on it).
Please read & supply "Information required when creating a discussion', for someone to offer further suggestions.
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.