@Fernando,
I have migrate my X99 machine from W10 21H1 to 21H2.
I am surprise that the BIOS Devices Option does no longer active. The F8 key option does no longer offer the Windows system disk.
If I plug any WinPE boot media the PC will mandatory boot directly from the USB, or if F8 is used only the USB device is present.
Do you have any idea and workaround to get back to the previous normal Boot option active situation ?

@Fernando,
Currently on ASUS Sabertooth X99 machine I am running W10 21H2 build 19044.1320.
I have done W10 21H1 to W10 21H2 migration via the NTLite Tool using the 'Check Update' option which offered me the W10 21H2 automatic migration procedure:



I am refering to BIOS Start menu, Boot Devices List.
When I have done the migration under W10 interface the "Secure Boot" option was enabled, is it the source of the problem ?

@Fernando,
YES, I can boot (W10 21H2) off the NVMe System SSD (i750) with no "Windows Boot Manager" listed on the BIOS Start Menu as you can see on the screenshot on post my #1
Disable CSM was setting
Disable "Fast Boot" and "CSM" does not change.
The system boot off any USB bootable when plugged in.
On the BIOS Start menu both the "Boot Option Priorities" and "Boot Override" options are greyed and inactivable !
What is your opinion to come back to a "Windows Boot Manager" and "Boot options" active ?

under uefi no need more than one BOOT LOADER "windows loader"
or must enable CSM boot "save + reboot bios" - this allowed FIXED priories or custom setup

some NVME not support for LEGACY - CSM is minimal support