Hello @Igor,
I´ve tried to copy /boot/boot.* to eMMC, but still no sucess on booting. (as @ATK )
As you explained that there is no magic (" u-boot , boot script which loads kernel") and the boot script seems fine to me (there are no differences between the script and scr file on eMMC, SD and HDD) the only part that could be wrong was the u-boot.
So, I decided to downgrade only the u-boot bin. I´ve downloaded the file linux-u-boot-orangepiplus-default_5.39_armhf.deb and extracted its content. Then I ran postinst script setting the device to install u-boot to /dev/mmcblk1 (eMMC, as I had booted from SD card).
Rebooting my OPi I noticed that the version of u-boot was really downgraded and the boot process was succesfully executed.
My guess is that something between 5.39 and 5.60 has broken the support on my hardware.
I´ve made some further investigations and noticed that it seems that in 5.60, the boot script, when running from eMMC, is not being able to read the /boot/armbianEnv.txt as I printed the env variables (env print) and the rootdev was still pointing to the wrong place.
I don´t know if it is possible, but I can try to trace the exactly version that breaks my boot support between 5.39 and 5.60. I just need to know where I can access these versions.
Best Regards.