Grub OS-Prober Disabled by Default on Arch and Most Derivatives Like Manjaro, Endevour, and others. I discovered this when I installed Endevour with grub.; The OS-Prober is disabled by default for security reasons. Here is how to enable it.
add or uncomment ( GRUB_DISABLE_OS_PROBER=false) in Grub Config file save that file then run
(sudo update-grub or sudo grub-mkconfig -o /boot/grub/grub.cfg) sudo update-grub did not work for me, but sudo grub-mkconfig -o /boot/grub/grub.cfg did work and now grubs os-prober and grub works.
Mel