This bios didn't work for me unfortunately. I flashed it using asus flackback, it took around 15 minutes (is that normal?) before it stopped flashing and accessing the flash drive.

Afterwards, I enabled other os and did the other thing mentioned in boot. I get an unable to boot device message.

Bios FlashBack procedure takes some time, depends on motherboard model, the led flash will increase his blinking rate till it stops.
Now it would be nice if u follow the instructions on bios/procedure settings here on point 4 [Guide] How to get full NVMe support for all Systems with an AMI UEFI BIOS