Using Win10 PC, I can successfully connect to a world on my child's Nintendo Switch.

My child cannot connect to a world running on my Win10 PC. The game and my Xbox ID show up just fine on the Switch as a cross-play game my child can (supposedly) join. Initiating the connection brings up the "connecting to multiplayer world" and proceeds no further.  Eventually an error is returned that the world cannot be joined and the connection timed out.

The fact that the connection works one-way, in my mind, eliminates many common issues, such as actually being friends, using the correct and same version of Bedrock, having Xbox permissions correct for a child account etc.

On the PC side I have tried firewall changes, router settings, and confirmed the "Xbox live multiplayer" "NAT type" and "server connectivity" are "open" and "connected" respectively. Quick note on "NAT type": sometimes when initially checking, I'll get the "Teredo is unable to qualify," but it always clears on a recheck.

Normally the switch and PC are behind the same router, but I even tried the Switch on a mobile hotspot with no change in behavior. Seems like the Switch doesn't even try and find the PC server, but without further diagnostic capability, I can't really tell which device is the issue. I've also tried invites, though they do not consistently come up on the Switch side. Even so, when they do work, the behavior is the same when accepting the invite.