On: Apple reveals App Store takedown demands by governments

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Not the OP, after some quick searching found this: https://github.com/HaarigerHarald/android-youtubeExtractor

Not open source, but "YouTube Downloader" (thread on XDA [1]) has worked well for me.

1: https://forum.xda-developers.com/showthread.php?t=2137743

Note that on iOS you can download videos from YouTube using youtube-dl (installed in Pythonista). With Pythonista's share sheet extension, it's quite convenient.