I ran some more tests:
– When I disable Parental Control, the Nintendo Switch goes to NAT Type B (the second best rating)
– if I also set up a DMZ (in Port Forwarding, send all external UDP ports to switch’s IP address) then I get NAT Type A (the best rating)
– as soon as I enable Parental Control, I get NAT Type D (multiplayer doesn’t work at all) regardless how the above is configured.
None of the settings in the uPnP section make any difference. (I can disable or enable the whole uPnP section and it doesn’t change anything.)
So does Parental Control block something that would affect Nintendo NAT? Because I kind of want the Switch (mainly a kids device) to have basic parental controls included on it.