Boot sequence from eMMC to SD-card

Please tell me, how change default boot device from eMMC to SD card on my VIM4?
I can’t find this topic on documentation.

i think need just write valid image to sd card and nothing special
SD card must have high priority

I think too, but, as I understand, there are no ubuntu images for SD for VIM4. It it true?

At this moment, Yes. We will upload SD images next month. But you can use fenix to build SD image now.