‘Secure Boot violation’ or ‘Operating System Loader signature found in SecureBoot exclusion database’ – Secure Boot no longer works.

Cause: Windows Update has blocked the Kasperksy Boot file used by agFM

Solution:

Go into UEFI BIOS setup options and clear the DBx key blacklist list.

OR – disable Secure Boot in the UEFI BIOS setup options

OR – convert your ISO (or any payload) to a .imgPTN23 file using the MPI Tool Kit (the payload must have a signed EFI boot file and support Secure Booting)

See https://rmprepusb.blogspot.com/2021/01/latest-windows-update-kb4535680-blocks.html