As far as I understand, the game offers single-player, local multiplayer (using multiple consoles and multiple game copies), and online multiplayer.
I have tested all available multiplayer options, both local (wireless) and online, but I was unable to get multiplayer working in any form.
In all cases, no lobby is shown for the second player/console, making it impossible to join a game.
I would also like to add that I purchased the game specifically for this multiplayer functionality,
as playing together offline/online was the main reason for my purchase.
The two consoles were running slightly different internal build versions:
Switch 1: 3.6.117.3733
Switch 2: 3.6.117.3735
Unfortunately, I did not have access to a second Nintendo Switch 2 with the exact same build version to verify whether multiplayer would work under identical versions.
At this point, I assume that we may need to wait for a fix,
and I sincerely hope that a bug fix or patch will be released soon,
as the multiplayer feature currently appears to be unusable despite correct setup.