Made some progress today. For debugging, I built my own image with the Edge kernel (6.18). However, this time, the board did not even boot up and there was also no signal on HDMI. The last idea I had was to downgrade the kernel using armbian-config. But since the Ethernet is not working, I was trying to setup WiFi because armbian-config was trying to load apt cache but without internet, I cannot load anything. After multiple reboots, I slowly cached the apt. Then the armbian-config loaded. I downgraded the kernel from 6.12.60 to 6.6.63 and then the Ethernet started working fine! ☺️
Current version:
$ uname -a
Linux rockpi.dev.com 6.6.63-current-rockchip64 #2 SMP PREEMPT Fri Nov 22 14:38:37 UTC 2024 aarch64 GNU/Linux
$ lsb_release -a
Distributor ID: Debian
Description: Armbian_community 26.2.0-trunk.44 trixie
Release: 13
Codename: trixie
I am now confident that somewhere after Kernel 6.6, the Ethernet is broken in Rockpi 4B.