Boot up your EnOS’ Live usb.
Launch Gparted and remove boot,esp flags from /dev/sda3.
Next, open a terminal and run the following commands:
1. sudo mount /dev/sda3 /mnt
2. sudo mount /dev/sda1 /mnt/boot/efi
3. sudo arch-chroot /mnt
4. grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=EndeavourOS-grub
5. grub-mkconfig -o /boot/grub/grub.cfg
6. exit
If you get any error messages at any of the steps above, please post them here on your next reply.
If all goes well, reboot your system.