Here is what worked for me and my setup. I did not need to downgrade grub, but I did need to run grub-install.
1: Boot into an EndeavourOS Live USB.
2: Open terminal
3: Check disks: sudo fdisk -l
Device Start End Sectors Size Type
/dev/nvme0n1p1 2048 2099199 2097152 1G EFI System
/dev/nvme0n1p2 2099200 2131967 32768 16M Microsoft reserved
/dev/nvme0n1p3 2131968 421529599 419397632 200G Microsoft basic data
/dev/nvme0n1p4 421529600 1470105599 1048576000 500G Microsoft basic data
/dev/nvme0n1p5 1470105600 1953525134 483419535 230.5G Linux filesystem
The above is my output:
nvme0n1p1 has type EFI System. This is the boot partition. This will be mounted to /mnt/boot/efi
nvme0n1p2, nvme0n1p3, and nvme0n1p4 are my Windows partitions. They are ignored because they still boot.
nvme0n1p5 has type Linux filesystem. This is the root partition. This will be mounted to /mnt
4: Mount disks:
sudo mount /dev/nvme0n1p5 /mnt
sudo mount /dev/nvme0n1p1 /mnt/boot/efi
5: Arch-chroot:
sudo arch-chroot /mnt
6: Check for my user:
ls home
should return adjagu for me, will be different for everyone.
7: Repair GRUB on EFI/UEFI:
sudo grub-mkconfig -o /boot/grub/grub.cfg
8: Reinstall GRUB on EFI/UEFI:
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=EndeavourOS-grub
9: Exit Arch-Chroot:
exit
10: Unmount mounts:
sudo umount /mnt/boot/efi
sudo umount /mnt
11: Reboot:
sudo reboot
After rebooting I choose EndeavourOS-grub from my computers BIOS UEFI boot menu.
Computer boots into the EndeavourOS boot loader (like it used to do before the last update) and all of my OS’s (including Windows) are available for selection.