I don't know anything about multiplayer, but could Minecraft be inadvertently checking to see if you have an active Nintendo Switch Online Membership when trying to connect to a LAN world?
I also have this issue, the standalone minecraft app is no longer in the Microsoft Store, it appears to be integrated into the new launcher.
Still here kinda, only it is the other way around in 1.17.40
I don't know anything about multiplayer, but could Minecraft be inadvertently checking to see if you have an active Nintendo Switch Online Membership when trying to connect to a LAN world?