reComputer J1010 - Can't Boot Custom SD Card Image

Hi everyone, I recently got a reComputer J1010 and I’m trying to use an SD card image that works fine on my Jetson Nano Dev Kit. It’s the Ubuntu 20.04 + JetPack 4.6.1 image from here:

I followed the instructions for SD card boot, but when I try it, the device doesn’t actually boot from the SD card. Instead, it seems to clone the eMMC system onto the SD card and continues using that.

What I want is to boot directly from my custom SD image, like I do on the Jetson Nano. Is that possible with the J1010?Any tips or suggestions would be really helpful.