Communities like GitHub - Free-TV/IPTV maintain free, publicly available playlists of legal, over-the-air, or internet-free channels.
Paid IPTV services provide customized M3U links or Xtream Codes for their subscribers. Download iptv4 m3u
M3U files are plain-text playlists containing URLs to live TV streams. You can find these from various sources: publicly available playlists of legal