Having raised the issue on the Community Forum regarding Secure Boot enabled being necessary for EFI Firmware updates (https://community.frame.work/t/firmware-updates-with-secure-boot-disabled/80586), the community replied that the page here on GitHub (https://github.com/FrameworkComputer/linux-docs/blob/main/misc/secure-boot.md) is wrong.
Specifically, it is said that this text:
"Remember. We advice leaving this enabled - disabling may lead to issues with our various upgrade processes. This also means it will interfere with EFI firmware updates if secure boot is disabled. So before you disable it, make sure you acknowledge this. No EFI updaters if secure boot is disabled."
is incorrect, and should be removed or corrected as appropriate.