@alex0 - Show me images of all stickers maybe it’s one one and you don’t notice, and be sure you looked all around/ON the LAN metal block, sometimes it hides on the bottom of that (towards PCIE slot). Look on back of board too, and also look on base of case, inside door of case, bottom of case etc.
It may be in BIOS, I’ve not dug around yet. But really, to find, I need to see all stickers from your board too, so I can see serial, or service/asset tag and use that to try and locate copy of MAC if stored as info/copy outside of GBE (sometimes is, sometimes not)
If you used this system recently too, and used it’s ethernet, you may be able to find MAC in router logs, if you can identify which MAC is this system.
I cannot make Ethernet work without correct original MAC ID