I hope this helps... For the TX3 Mini, I used the distributions listed on https://www.armbian.com/amlogic-s9xx-tv-box/. Here's what I did:
* Create a bootable image using Rufus (following the instructions).
* Once the image was created, I went to the SD card's storage drive on a PC and made the following changes:
* In the root directory of the SD card, I copied the file u-boot-s905x-s912 and pasted it as u-boot.ext.
* In extlinux\extlinux.conf, on line 4, I changed it to "fdt /dtb/amlogic/meson-gxl-s905w-tx3-mini.dtb".
* I ejected the SD card, inserted it into the TX3 Mini, and turned it on.
If it doesn't work, try a different distribution.