Hi, I thought my post had been lost due to me forgetfully rebooting.
I can access “watch.plex.tv” in a browser. I forgot to mention however that all my posters show when connected to “https://app.plex.tv/desktop/” but not when connected via local host “http://127.0.0.1:32400/web/index.html#!/” which is my usual method by double-clicking plex Media Server in system tray.
It is a policy in your web browser which prevents the display.
The Plex web app is loaded using an unsecure connection (that is the http part of the URL)
While all data in the Watchlist are stored on plex.tv, from where they are loaded over an encrypted connection (https).
It is this mixing of unsecure and secure connections on the same “web page” which your web browser is taking offense at.
Therefore the recommendation is to always use the hosted web app (or other native Plex apps). The local web app is only for setting up Plex and for the case of an internet outage. (during an internet outage the Watchlist is not available anyway)