Elclaudio

OK I FOUND THE CULPRIT ! the issue come from UBOOT like I imagined. After installing older uboot ETH0 worked straight away
Since I couldn't find the uboot .deb used in my old armbian 5.95 in https://imola.armbian.com/apt/pool/main/l/
I took the uboot files from my WORKING armbian version kernel 4.19.69 in /usr/lib/ linux-u-boot-next-odroidc2_5.95_arm64
there should be 2 files : bl1.bin.hardkernel  and u-boot.bin
copy them wherever you want on the latest armbian (currently in test : Armbian 21.02.2 Buster with Linux 5.10.16-meson64,) Linux odroidc2 5.10.16-meson64 #21.02.2 SMP PREEMPT Sun Feb 14 21:50:52 CET 2021 aarch64 GNU/Linux
I backed up the original files in the same directory with .ORI extension
Then I run the commands here
 
If you do it beware with dd it could crash your partition if missused, also adapt the paths and filename to your particular case.
 
#!/bin/bash # install older uboot from armbian kernel 4.19.69 dd if=/root/uboot/bl1.bin.hardkernel.OLD of=/dev/mmcblk0 bs=1 count=442 conv=fsync > /dev/null 2>&1; dd if=/root/uboot/bl1.bin.hardkernel.OLD of=/dev/mmcblk0 bs=512 skip=1 seek=1 conv=fsync > /dev/null 2>&1; dd if=/root/uboot/u-boot.bin.OLD of=/dev/mmcblk0 bs=512 seek=97 conv=fsync > /dev/null 2>&1 # restore original uboot #dd if=/root/uboot/bl1.bin.hardkernel.ORI of=/dev/mmcblk0 bs=1 count=442 conv=fsync > /dev/null 2>&1; #dd if=/root/uboot/bl1.bin.hardkernel.ORI of=/dev/mmcblk0 bs=512 skip=1 seek=1 conv=fsync > /dev/null 2>&1; #dd if=/root/uboot/u-boot.bin.ORI of=/dev/mmcblk0 bs=512 seek=97 conv=fsync > /dev/null 2>&1  
It would be nice now to debug what's gone wrong with uboot code...