@prahal ok - so I've only been using the micro SD card to try boot and load an image from. So far, from what I understand, RoobiOS seems to be installed on the onboard emmc at a lower-priority boot option (i.e. if there's no boot OS on the NVMe, microSD or SATA III drive then boot from the onboard emmc).
If I understand correctly, you're suggesting I load an empty / non-bootable micro SD card and then from the RoobiOS menu select one of your builds, chose to install to the micro SD and then transfer the bootable image to NVMe after? (Not that I know how to transfer the OS from micro SD to NVMe ... yet ... but, as I say ... more learning ) . If this is correct then happy to try that.