Thanks @SteeMan i am using "Raspberry Pi Imager" which worked well. However, after some more troubleshooting and copying u-boot-s905x-s912 file to u-boot.ext, the box is now booting with Armbian_20.10_Arm-64_focal_current_5.9.0_desktop.img .
But again no network, and i noticed, its same issue with all other images i tried when using u-boot-s905x-s912
dmesg error:
ethernet eth0: no phy at addr -1
ethernet eth0: stmmac_open: Cannot attach to PHY (error: -19)
Followed but no luck.
files on SD card looks like as per screenshot below on working old image (Armbian_5.37_S9xxx_Ubuntu_xenial_3.14.29_mate_20171226.img) with network that does not have kernel headers,
So i am not able to figured out which file is the u-boot, or which files i should replaced in new image (from working image) in order to boot with network interface?