I attempted to do this. I was going to rsync from the eMMc to the NVMe, update the config file to mount the nvme as the root device and the emmc boot on /boot

I can't mount the EMMc . The partition table indicate type 83 which is Linux. I tried ext2, ext3, ext4, and squashfs. No luck
Do you have a procedure to move the root filesystem from the emmc to nvme ?