Windows Player not visible to other Plex applications on the same LAN

Plex Players Desktop Players
2

Are you using “host network” for the container? Plex companion needs a running server in the same network segment as the two client apps.
If the container uses “bridged” network, this is not the case.
Can you remote control the web app oin that PC?

Update to server 1.20.3: Plex Media Server - #369 by gbooker02