I’m currently experiencing an issue I’m trying to fully solve, but seems for me I cannot join LAN sessions while Steam is running.
It connects to LAN in PIE, I see broadcasts, but between 2 instances of game standalone or packaged.
After digging around and a restart it worked, then after a bit it didn’t again. All I had done was launch Steam and Discord. So I quit both and it worked again. Launched one at a time and turns out if I have Steam running it wont LAN connect.
So, while it’s not an ultimate fix (and I got here Googling issue) you could try closing Steam and seeing if that gets your LAN session working. Saves doing what I was doing, chasing code and pulling out old projects to find out even earliest ones don’t work.