There's a large number of legal IPTV streams -- a lot of them are just the streams you would normally be able to access via Pluto, Plex, and other services. There's also a lot of public access/public media channels are legit and free All of the ones available at the link I posted should be legal. There are "pirate" IPTV streams out there, but I don't know any off the top of my head. I would check with the c/piracy community.
The really tricky part is getting an Electronic Program Guide (EPG) for free. Very few EPG providers are willing to give that away. You can roll your own for free but it's complicated enough that I basically gave up on it.