This will obviously make the app worse but for now there is no other solution. Whatever YouTube plans to do with the current Watch Later functionality is unknown. Maybe there will be a similar new functionality on YouTube at some point and even an API for it...
The changes in this PR add user playlist selection to have a way of this app still making sense after the API shut down (see https://github.com/lambdasoup/watchlater/issues/53).
This will obviously make the app worse but for now there is no other solution. Whatever YouTube plans to do with the current Watch Later functionality is unknown. Maybe there will be a similar new functionality on YouTube at some point and even an API for it...