Secure Boot does not even come supported out of the box in Qubes.
" Is Secure Boot supported?
UEFI Secure Boot is not supported out of the box as UEFI support in Xen is very basic. Arguably secure boot reliance on UEFI integrity is not the best design. The relevant binaries (shim.efi, xen.efi, kernel / initramfs) are not signed by the Qubes Team and secure boot has not been tested."
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