Just completed EndeavourOS installation but on reboot I have lost my Windows 11 OS.
I am running Endeavour OS on one nvme drive and Windows 11 on another smaller nvme. I chose the Grub Boot as I’ve used that on several Ubuntu distros and had no problems with it identifying my Windows 11 but not this time.
Can anyone give me some guidance on how to fix the issue.
TIA … Dave
Welcome to the forum 
Could be caused by the fact that os-prober is not set in the grub config file.
See the link below , and scroll down to the text below the bold i to solve this.
https://discovery.endeavouros.com/system-rescue/repair-a-non-booting-grub/2021/03/
Enable os-prober and rebuild grub.cfg it should add it if not could be windows using legacy mode instead of EFI …