400mhz is 'out of the box' setting, according to the user guide (safety feature for first time setup maybe ?).
Are bios/chipset drivers up to date, do you have version 1.2 of RM ?
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.