You must either make the sda device unbootable by removing grub from /dev/sda or force the UEFI-BIOS to boot from the nvme drive (or disable the possibility to boot from /dev/sda in UEFI-BIOS itself).
You must either make the sda device unbootable by removing grub from /dev/sda or force the UEFI-BIOS to boot from the nvme drive (or disable the possibility to boot from /dev/sda in UEFI-BIOS itself).