I have configured my kickstarter Bolt V8 with a 1TB Sabrent 2280 drive in the M2 Key M slot. On this, I have installed gentoo with the standard partition configuration. Everything was working OK, but I was still using the original BIOS which came on the device. I then created the EFI USB to update the BIOS to 1.08, which went as planned. Now when I look in the boot options, the nvme drive is no longer an option. The drive is recognised - it is listed in the EFI shell list of drives, and also if I boot from USB I can mount the nvme partitions and access them without any issues. The Sabrent drive is also listed under the BIOS advanced/nvme item. Is my experience normal - has the nvme drive been removed from the boot options? If so, is that a temporary change or permanent? Thanks for your comments!
OK - now I have worked this ou, so I share it here in case anyone else has the same problem. The only devices which are visible in the boot priority menu are those which are recognised as bootable. Although I had been successfully booting from the nvme drive with the original bios, it wasn't being recognised as bootable following the bios update. I also confirmed the 1.07 bios, and the result was the same. I then booted and chrooted into my environment, and re-installed the EFI code for booting, but this time with the --removable option (as explained here: https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Bootloader). Now I have an option in the boot priority menu to boot my gentoo installation, and everything works as planned.
