Thanks for the output!
In the live session, you would need to mount your root partition first and then the ESP.
Also make sure you are connected to Internet.
Open a terminal and:
1. sudo su
2. mount /dev/nvme0n1p2 /mnt
3. mount /dev/nvme0n1p1 /mnt/boot/efi
4. arch-chroot /mnt
5. pacman -Syu ## to update your system
6. pacman -S grub ## to re-install Grub
7. grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=EndeavourOS
8. grub-mkconfig -o /boot/grub/grub.cfg
9. exit ## to quit chroot
Hopefully this will resolve the issue.
If you get any error messages at any step please post it on the forum.
Good luck!
Edit- Inserting the important command arch-chroot /mnt 