I only booted to CoreELEC and LibreELEC from the external SD card. Never installed to the eMMc. I have been using the latest images and that is probably why I didn't find the "u-boot-s905x-s912" file in them.
Thanks to you, I managed to boot using the Armbian_20.10_Arm-64_focal_current_5.9.0.img.xz image. Ethernet is working, but there is no wlan0. dmesg shows the wifi device as "TLL901X".
Can you suggest any other distro where wifi is functioning, it doesn't have to be armbian or latest?
Sorry for the late reply. I am still stuck with 1 post a day.