Switch local wireless multiplayer mode stopped working after 26.21 update

The recent Bedrock Edition 26.21 for Nintendo Switch appears to have broken local wireless multiplayer.
When playing in local wireless mode, you cannot see each others worlds to join as usual, nor can you see your friends playing to join their game. Local multiplayer for Switch just no longer functions.

We are playing one person on Switch 2 and one person on Switch 1. Previously until the 26.21 patch, this worked no problem.

I have tried all of below the fixes found online so far:

Ensuring both Switches have the same version of Minecraft running.
Ensuring  we are both in "Local" mode, not online.
Clearing marketplace and download caches via the storage menu.
Ensuring we are both Nintendo Switch friends.
Completely deleting Minecraft and reinstalling to the Switches.

None of this resolves the issue.

Expected result would be to be able to see an join each other playing over local wireless mode on Switch.

Actual result is we cannot play together or even see each other in game.

What is weird is that when in the switch console menus, we can see each other playing Minecraft, and can click to join/launch Minecraft from the friend list when one of the players is actively playing Minecraft, but when the game boots up, local multiplayer still does not work when in local mode, nor display friends playing on the same local network or show their world to join.

Any help on this would be hugely appreciated. Playing local multiplayer Minecraft on Switch with my son has been a huge part of our lives for many years, and now that it no longer works it feels like a huge loss.

Kind regards,
Ben