Hi again Werner. Please excuse the long waiting time. It's taken me a long time to place back the device at its intended location. Here's the requested output.
https://paste.armbian.com/alefaladep
At the moment I've got it running on a realtek usb-ethernet dongle at full speed (confirmed throughput up to about 300Mbit). Last year when I created the thread we were using the Nanopi Neo4's onboard realtek ethernet port. No matter what we did it wouldn't run at speeds over 10Mbit. And no, the port isn't faulty. It's happening on ALL armbian devices (official and unofficial) on current distributions still to this day. Bookworm/Trixie/Noble/Jammy, with kernels 6.12, 6.6, 6.1 and 5.15 tested. On x86 debian it works right out of the box at full speed and we're talking much weaker hardware (Intel z8350).
Thanks for your work. Armbian is definitely the future IMO.
Mike H's post in Ethernet throughput issues on armbian (at high latency) was marked as the answer