Try rapidly tapping the Del key (and F2 is the alternative, if I remember correctly, for small keyboards) immediately after power on. Push the power button, then just rapidly keep hitting Del until you either get the BIOS or something else happens.
I had the same thought so did disconnect one of my two monitors without luck. But I figured out a solution.
I pulled the nvme that Windows is installed on.
Instantly on reboot I see the asus splash screen and got into bios
I booted into memtest86 from there and that will run until the AM. Then I can see with fastboot off if I can get into bios with the nvme back in.
I have the same issue on the B650E-F motherboard with the AMD 7900X processor, I can't get to the bios either (current version 822). I've downloaded a newer version, but not being able to get to the BIOS makes updating it difficult.
Second reason why I want to boot into BIOS is that I have 2 NVME drives installed and use the BIOS to select which one to boot from. After spending an hour trying to get into BIOS the normal way (holding/tapping DEL or F2 keys) which just extends the boot process to several minutes, I ripped out the first NVME drive to be able to boot to the second. Otherwise it boots "just fine" to the first one...
Next to try is remove both drives so there is no Windows to boot into.