I found this and I think my problem is that I have not activated multi boot.
In order to bootup from SD/USB images, you need Android (V180209 or newer) or Ubuntu (V180531 or newer) running on your eMMC with Multi-Boot activated.
I also found this
In order to boot images from external media you must make sure:
* Android is running on the eMMC
* Activate the Multi-Boot
For different images you may need different Android versions.
* LibreELEC / Ubuntu with Linux 3.14: You need Android M or the latest Android N (V180207 or later) running on the eMMC.
* Ubuntu with Linux 4.9: You need Android O running on the eMMC.
And the VIM also support dual booting mode from both onboard eMMC or SD card, we design a Function button to support booting mode chose as following:
* power on without pressing the Function button, will normally boot from onboard eMMC
* power on and pressing the Function button, will boot from the SD card.
I tried to use multi-boot with the function keys but I could not do it because it does not even boot me on EMMC … it’s a shame I can not try the new releases of ubuntu on SD