oooh welcome to the cant boot up after bios update club, get ready to rollback your bios with an old hard drive with windows, your new bios will not boot up with an SSD.
here are the steps to roll back your bios.
I am also affected by this, same laptop. With FW 3.06, the system would not boot anymore until I took out the M.2 Sata SSD.
I'm sure I've wasted over half a day to come up with a solution for this cluster-f*ck (open laptop, take out M.2 and HDD, put in an old HDD and reinstall W10, flash back old 3.02 BIOS, disable Firmware Device in Control Panel, etc. ) But that stupid Windows Update would just reapply the BIOS-Upgrade after every reboot. After around 5 iterations of trying different things I gave up.
I opened a ticket at Asus Support, but of course they were worthless. The only reply I received was that I am out of warranty....
Fast forward to yesterday, when I by chance tried to use a NVMe M.2 SSD and voilà, this worked, the system is booting again!
So now instead of a $1500 brick I have a working system again, thank god.
It's sad to say, but I can not really recommend Asus wholeheartedly anymore... after the power drainage fiasco and now this ... their support is really lousy and QA seems to be next to non-existant.
And Asus help desk is ZERO help. I can roll the computer back to 3.02 BUT windows insists upon installing 3.06 on next reboot, and while I have suspended updates, I cannot seem to find the option (via show/hide.cab file) that keeps it from automatically installing 3.06 on the next start up. I've asked ASUS for an updated bios that bypasses the 3.06 junk (they won't), and I am unable to keep this BIOS from being loaded. Any guidance you all may have would be appreciated.