I have a tried and tested solution. You need to change the Android TV 10 OS to an older version of Android TV 9. Then you will be able to boot CoreELEC. I’m sending a link to IMG and tools. http://kodi.pilsfree.tv/img/androidtv/km9pro2gbddr3v13/
Attention, this IMG is for version km9pro classic v.1.2 - 1.3 (2GB DDR3)
It may throw an error at the end of the conversion. That’s right, it turns off the tool and the AndroidTV 9 OS starts up.