It hasn't been mandated at all. A number of years ago, Microsoft made headlines by changing their policy to get rid of that mandate. See https://arstechnica.c

It hasn't been mandated at all. A number of years ago, Microsoft made headlines by changing their policy to get rid of that mandate. See https://arstechnica.com/information-technology/2015/03/windows-10-to-make-the-secure-boot-alt-os-lock-out-a-reality/ https://arstechnica.com/information-technology/2015/03/windo... . Microsoft's page at https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/disabling-secure-boot https://docs.microsoft.com/en-us/windows-hardware/manufactur... says that you can "usually" disable it, so I don't think they've changed their policy since then.