You literally just forked Video Background Play Fix, gave it a “New name, id and icon”, and nothing else.
Did we look at the same diff? https://github.com/lagudafuadtosin/plays-on/commit/95aed0ca49074f2477aa597038346ad8e885686f clearly has functional changes. Scroll past breaking the various translations and you'll see some changes in video-bg-play-content.js:

I can't tell you if this extension actually works but Video Background Play Fix did not work for playlists for me in the past (that was before I discovered Vanced).