grub-install defaults to a specific path. This is explained in the GRUB manual. See here:
https://www.gnu.org/software/grub/manual/grub/grub.html#Installing-GRUB-using-grub_002dinstall
On EFI systems for fixed disk install you have to mount EFI System Partition. If you mount it at /boot/efi then you don’t need any special arguments:
# grub-installOtherwise you need to specify where your EFI System partition is mounted:
# grub-install --efi-directory=/mnt/efi
Now guess what mountpoint is used by default in EndeavourOS.