Please stick to the rules for feature suggestion and go with 1 suggestion per thread. Otherwise users can only vote for the full package, either forcing them to vote for stuff they don’t want for the sake of another included suggestion or getting no votes because users don’t support the package in its entirety).
As for your suggestions…
You should already be able to do that for most hubs linked to your own or shared libraries (Continue Watching is probably an exception and cannot be removed); the hubs from Plex’ Discover or video-on-demand services are indeed linked to those services being pinned to the sidebar.
https://support.plex.tv/articles/manage-recommendations/
You can already do that using smart collections.
https://support.plex.tv/articles/publishing-collections/
There’s already a number of related suggestions, discussing that option
- I don't want to see watched content in my suggested line up
- Customize discovery and Toggle on and off what I already have
Though I couldn’t find a request/suggestion discussing a particular option/filter to hide watched items from search.
There’s already an existing feature suggestion discussing an option/preference to hide Plex’ on-demand media from the search.
If you don’t want to use Plex online media sources, you can disable them for good and they won’t show in the search results to start with.
https://app.plex.tv/desktop/#!/settings/online-media-sources
Those seem to be unique suggestions (at least I couldn’t find existing suggestions specifically focusing on those topics).
You can enable notifications for items on your watchlist being available on a selected streaming provider.
You should already have a hub Available from your Watchlist if Discover is pinned to the sidebar.
