pebcak
10
Archlinux and by extension EndeavourOS don’t support Secure Boot.
There is however a way to implement it involving some, speaking for myself, rather advanced CLI Fu:
https://wiki.archlinux.org/title/Unified_Extensible_Firmware_Interface/Secure_Boot#Implementing_Secure_Boot
There are also a couple of threads discussing Secure Boot on the forum like the one below: