suddenly can’t add my media, keep getting a message to download plex server, but it’s already downloaded and installed
That is the screen of an account that has no plex server of its own, or access to one. Double check which account you are logged in as, to make sure it is the same as the server’s account.
If you are logged in correctly, check to see if your server somehow got unclaimed.
The server on your user account has been seen last by plex.tv ~8 days ago.
Try to remember what happened around that time.
