I just flashed my Bios with an old (2016) insydeH20 bios and that was dumb-got the error “no bootable device”. I replaced the original her with an sdd a year or so back so changed the boot order, didn’t work. Here’s what WILL get you back to bootable.
When restarting hit whatever f (function) button to get to setup start up screen, arrow right to the last screen and change windows boot to LEGACY. Windows 8 and above warning blah blah then save and restart. Got me back to my original sdd/operating programs so I could flash with a more updated Bios firmware.