I'm using Win10 and I'm not able to boot into BIOS, nor by hitting F2 or DEL while booting neither with the Windows 10 option: "Recovery / Advanced Setup / Troubleshoot / Advanced options / UEFI Firmware Settings "(this just boots the system back into Win10).
I'm using an ASUS PRIME B550-PLUS Mainboard with the newest Firmware (Version 1401).
"Turn on fast startup" in Windows is disabled, but this was also tested with fast startup "on".
HW/ SW:
CPU: Ryzen 7 5800x
MB: ASUS PRIME B550-PLUS
M2: Kingston A2000 1TB
OS: Windows 10 Pro