All clear!
Your memory is spot on!
Port 3 = LAN2 = eth1
Port 4 = LAN1 = eth2
But SSH access is still needed to change the “tagged” “untagged” condition of the ports, since the Switch section is complaining about the topology, am I right?
Is there a way in the owrt GUI to set this, or the only way is modifying the /etc/config/network file (with WinSCP, for example)?