I would advice against using downloaders and addons as they constitutie a privacy concern. However, sometimes you need to as the below program is not allowed access.

On a laptop in terminal:

wget + settings + link

Or better

Use: youtube-dl -f best youtubelink

Or youtube-dl -F youtubelink to find the possible formats.

If you need to convert a video, then use ffmpeg.

Consult howto download these programs and howto use it ( man pages)

For Android: you van run a linux instance on your Android with Linux deploy or something. Check privacy and trackers.