Kwiboo I have a RK3399 box (X99) for which I had a working 4.4 dts. I tried booting the rockpro64 img, but it gave an error wrt i2c on the serial console.
I ended up modifying the original 4.4 dts which got rid of the i2c error bringing it closer to rockpro64, but the screen is blank. There is an error regarding EDID is blank.
Let me know so I can provide any debug logs or dump of any parameters from serial console.
You will need a 5.1 not 4.4 dts kernel file to test with mainline images used here.
But I can't help further.