Look on the Yandex share in the first post, familiarize yourself with the structure in there and also the instructions in the first post. You need to download both the xz file that you need, plus the TX6 uboot, I used the one from July. I used balenaEtcher to write the xz to the sdcard, then again balenaEtcher just for the uboot (since it places it in the boot area of the card). Then it booted on my Allwinner H6 box. Without writing the uboot on the card, it didn't work. The instructions do not emphasize this too much and I expected that I place uboot as a file in the boot folder (as for Amlogic for example).
Wow this sounds bad. With the original Android, using a terminal I got the full amount of RAM when running the "free" command.