Hi, the Rescue System’s u-boot (on eMMC, /dev/mmcblk0boot0) does not use /sbin/reform-init, that’s why it does not respect /reform-boot-medium.
To work around this, flash this alternative build of u-boot onto the eMMC boot partition: A variant that uses /sbin/reform-init in the eMMC boot sequence, allowing to boot from NVMe via eMMC · Reform / reform-boundary-uboot · GitLab