"How to use the dedicated server" bedrock_server_how_to.html is out of date.  Could you please update the part about of UWP loopback restrictions?

cmd> CheckNetIsolation.exe LoopbackExempt -a -p=S-1-15-2-1958404141-86561845-1752920682-3514627264-368642714-62675701-733520436
Error: Invalid Parameters

The workable way: 

1. Find the current Minecraft appx package name
   PS > Get-AppxPackage | Select-String -Pattern "Minecraft"
   Microsoft.MinecraftUWP_1.19.4101.0_x648wekyb3d8bbwe

1. Invoke CheckNetIsolation with the name of Minecraft package.
   PS > CheckNetIsolation LoopbackExempt -a -n="Microsoft.MinecraftUWP_8wekyb3d8bbwe"

OK.