Implement like / favorite / star button

You can already do that…
Create a smart collection based on an advanced filter (e.g. w/ rating > 4 stars and whatever other criteria you want to apply). Then publish that smart collection to your library “recommended” tab or the server home page.

https://support.plex.tv/articles/publishing-collections/

Edit:
As for the suggestion title… having a “favorite” button has already been requested in a separate thread.