Had the same error. I fixed it, using my Ventoy stick like that:
Stick in Ventoy USB, reset, choose Manjaro (or any Linux), choose Boot in normal mode, choose detect EFI bootloaders, choose (hd1,gpt1)/efi/Manjaro/grubx64.efi
System should boot, if not, try again with an entry below.
At the Command line:
sudo cp /boot/efi/EFI/Manjaro/grubx64.efi /boot/efi/EFI/boot/bootx64.efi
sudo update-grub
done