In bios advanced settings, you should have Boot (header), boot options (numbered or drop down list) where you have change boot order/disable options.
I don't have asus board, may be better if you post on https://rog.asus.com/forum/forum.php#
Someone there can probably walk you through it(or point you to a pictorial/video tutorial).
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.