@jock and @MattWestB, I did too, a fast test in my MXQ_R2B_LP3, i replaced only rk322x-box.dtb from Multitool in my sdcard with my configuration, i use Armbian Buster legacy, and HDMI worked! Yet couldn't install it in emmc!
Thank you very much for your dedication and commitment, I would like to help more, but I don't have that ability!