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-prober and build it yourself:
Download and extract the zip file. Go into the folder os-prober-master and open a terminal in there.
In the the terminal, run
makepkg -s
When it is done, install the package with:
sudo pacman -U os-prober-1.81-1-x86_64.pkg.tar.zst
Another option would be to skip the above and create a custom.cfg file in your Hyprland’s /boot/grub and copy the menuentries from your Plasma’s /boot/grub/grub.cfg into it. This will add boot menu entries from your Plasma to your Hyprland’s Grub boot menu.
I suppose this one is the EFI entry for your Hyprland. This uses the bootloader installed in the fallback path. You could try installing GRUBX64.EFI into the normal path if you want:
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=enos-hyprland
We can try removing Widows EFI entry:
sudo efibootmgr -b 0000 -B
Please consider the suggestions above and if there is anything unclear or you have other questions, post about it back here.