A Phoenix Labs account is free and doesn't require giving up personal information; all you have to do is connect it to your Steam ID. I don't have a Nintendo account or a Switch and thus can't test it, but as far as I know you don't need a paid Nintendo account to be able to connect it to a Phoenix Labs account. Are you sure you didn't miss an option somewhere?

Originally posted by Trollblume:

I was very dissapointed to find out that without a phoenix account and a nintendo online payed subscription it is not possible to play a local / LAN game with Nintendo Switch and Steam Deck/PC together.

Hope it will be added.

Account is free to make ... Just do it.

yeah they failed it a lot game cannot be played offline in lan.. like losing housands of new players who will to buy game for local play and even moding it for split-screen to play in one pc with wife/son whoever.
insecurities over quality