

Except you technically can. Windows 11 registry allows for installation without secure boot and its called after the upgrade process, thats what things like rufus patch to allow it.
Now idk if secure boot has to be enabled for windows 10 to consider it upgrade ready, but its technically all in there
… Secure boot has nothing to do with encryption and your data. Bitlocker can work without secure boot https://superuser.com/questions/1200958/does-enabling-bitlocker-require-secureboot