EndeavourOS grub does not detect Arch Linux

[pebcak]

Have a look at the first part of the following post regarding os-prober and systems on Btrfs:

Phantom windows just won't go

We can try tackling the issue in bites and pieces to see where we land. First, if I remember correctly, quite a while back when I was experimenting with multiboot system on Btrfs and Grub, the regular os-prober was incapable of detecting other systems. I had to use one specifically patched for Btrfs. Back then I used Manjaro’s os-prober which has a fix for this. There is a package os-prober-btrfs in AUR but that one hasn’t seen an update for some time. I would suggest to download Manjaro’s os…