I had the same problem. The network card in TrueNAS Scale 25.04.x was detected but couldn’t connect to the switch.
The card was connected to the switch using an SFP+ 5Gbps (LG-5GE-SFP) insert. It has a lower temperature than the SFP+ 10Gbps 30m, hence this choice…
On the switch it was visible that the network card was trying to establish a connection at a speed of 1000Mbps - but it was unsuccessful and the attempt was repeated from time to time.
The problem turned out to be that EEE (Energy-Efficient Ethernet) was enabled in the network card.
EEE can be disabled like this: ethtool --set-eee interface_name eee off
To avoid the need to manually run ethtool after each computer startup, I added a command to “System->Advanced Settings->Init/Shutdown Scripts”
