Took me awhile to sort through this one, as it involved questions of bios versions, Q-Flash, clearing CMOS, bios-setting experimentation, much swearing and hair pulling. Check my Sig below for my system details. Short of it is that the only issue I've had with my new Aorus Master x570 & my new R5-3600X & my 50th Ann 5700XT (PCIe4) is as follows:
If the discrete GPU is configured in the bios either as PCIe4 (Gen4), or "Auto", the Master board bios versions F3, F4, and F5g (tested them all vigorously thus far) most of the time during each boot attempt, especially each warm boot attempt, fail to recognize the GPU as the boot device to initialize. What happens is that the boot attempts fail because no GPU is initialized and so no output signal to the monitor occurs, even though the boot process often starts and finishes independently, all the way to the Windows desktop, even though the boot session is itself futile since no GPU output signal to a display device is generated (since no GPU initialization occurred during the boot process) and so no GUI or CLI interaction with the booted OS desktop is possible. At this point only a system reboot/restart via system hardware switch is possible.
Result: It appears as if the system so affected cannot boot because no GPU is initialized and so no GPU sends the necessary signal to the attached, desired monitor.
Easy Workaround. My own testing thus far has shown this method to be 100% reliable on my system. In the bios, simply set the GPU configuration to PCIe 3.x--or PCIeGen3--save the settings and reboot the system. Henceforth, all subsequent boots and reboots should occur as expected and without incident as the GPU will initialize.
Caveat. Of course, this is ultimately unsatisfactory since the the GPU is operating only in PCIe3 mode and not in PCIe4 mode, as it should be.
Solution: Gigabyte needs to fix this in the bios!
Edit: It appears that with bios F4 the system is now warm and cold booting with PCIe set to Gen4. Warm booting, however, seems to take far too long. It's almost like I had to "train" the bios with my PCIe4 GPU! At least it is working reliably now. F4 also provides proper boost for my 3600X. (F5g does not.)