Not the OP, but I have a Postfix mail server running on my home media box that receives YouTube URLs sent to its special email address. Postfix passes the message to a Python script that parses out the URL and places it into a Redis queue. A second Python program, running as a daemon, watches the queue and then downloads the video using yt-dlp. I can also enqueue video URLs from the command line.

This is the command that the daemon runs to request 720p, for example:

    command = 'yt-dlp --write-info-json -f "bv*[height<=720]+ba" --output "out.%%(ext)s" --merge-output-format mp4 "%s"' % url

I run a flask app with an endpoint that takes a video URL and runs yt-dlp. I have a bookmarklet that submits the URL of the current video page I'm on to the web service.

Also when I'm in NewPipe on the phone I can go to a video and share the URL to an app that forwards it to the web service.

yt-dlp

I just parse the URLs from the liked playlist every couple of days with a Chrome extension then simply run the app.

yt-dlp would work automatically too with logins but I'm always too nervous that Google would just straight up ban my account for whatever reasons. So I rather do it in a more manual way.