Taking inspiration from this post from 2023 for a static IPv4 address I would probably try something like this:
sudo nmcli device
sudo nmcli device show
sudo nmcli con add type ethernet con-name myrouter-static-eth ifname end0 ip4 192.168.0.100/24 gw4 192.168.0.1
sudo nmcli con mod myrouter-static-eth ipv4.dns "1.1.1.1,8.8.8.8,9.9.9.9,208.67.222.222"
sudo nmcli con up myrouter-static-eth
sudo nmcli device show
I think that the older images used end0 and end1 instead of eth0 and eth1 (you can probably confirm that with sudo nmcli device). The commands I gave above are more of a general gist of what you might need to do (for a static IP) than the exact details for your specific case. If you already know how to use ifconfig, you should be able to workout how to use the network manager command line interface.
I guess from here that you are using StarFive Debian, probably a version from before 2024. Its latest version is Debian 202510, maybe you can try flashing the new version.
The new version is on the left side here. Debian 202510 requires using the new U-Boot SPL.
I thought about it again, Debian now doesn’t use ifconfig to set up the network by default; you should use tools like ip add or nmtui.
