Josh Centers for TidBITS:
There are several reasons why you may want to download videos from YouTube. Like most cloud-based things, YouTube videos can be ephemeral. Videos disappear all the time for all kinds of reasons: The uploader pulls it down, copyright restrictions (sometimes legitimate, sometimes not), and YouTube's ever-changing and seemingly random standards of acceptable content. But conservation is not the only reason people download YouTube videos. For example, they may want to download a clip to be used in their own videos (respect copyright, of course).
Note that downloading YouTube videos with a tool other than YouTube's own apps (which requires a YouTube Premium subscription) violates YouTube's terms of service … Having said that, I've never heard of YouTube punishing a user for Downloading videos, even if he uses copyrighted material in videos you upload to YouTube, can get you into trouble.
MacDailyNews Take: Throughout the article, centers cover four tools that you can use to download YouTube videos in macOS:
4K Video Downloader
Do you have a favorite?