Even though you said there are no "vendor-lockin" i felt like so that's why i created a post on this forum as this issue came only after armbian os flash.
As i said, after flashing armbian os, i was not able to use MASK button to bypass emmc boot and about a dozen of different os other than armbian failed to boot from SD card.
Then i experimented on different methods including the PC connectivity but changing bootloader or os image didn't work as the mask communication is getting lost during flash command run.
I deleted boot files from armbian boot partition to check if that fall back to SD card, but there was no luck. However armbian SD card boot still worked.
So i confirmed that it is the change in bootloader that armbian made.
Then i re installed armbian os inside emmc and used dd command to write the original bootloader images which is taken from the nanopi r6s official eflasher download link.
It worked!
Now i am able to install other os than armbian.
Kindly fix this issue and acknowledge the same, otherwise people like me will think twice before testing latest armbian os next time.
