If you remove the online services in your account settings those’ll be gone from every client. This has been true for years now, but you could remove a lot of it via client options until New Experience so it wasn’t that well promoted (particularly as Plex doesn’t want you turning that off really). Doing it this way will actually remove even more of it than the client options did.
Go here: https://app.plex.tv/desktop/#!/settings/online-media-sources turn all those services off.
Here’s a Topic someone put together with screenshot and more detail: At least a little help for Roku Users
Once you turn all those off, Plex is pretty much “local only”.
