I don’t feel comfortable making recommendations about this, because I don’t watching RPG livestreams or actual plays. Why? Because I don’t particularly like them.
Now, that doesn’t mean they’re not good; it just means they’re not for me. I, personally, don’t find it particularly enjoyable to watch other people play a game. I enjoyed Wil Wheaton’s Tabletop series. I thought it did a good job explaining how the featured board games worked. Critical Role is hugely popular and has made RPG fans of people who don’t actual play the games themselves. They’ve done a great job of bringing awareness of the hobby mainstream. Obviously, a lot of people enjoy watching livestreams or RPG actual plays and/or find something of value in them.
I suppose they could be good at figuring out how a system works, but I think you’d have to either watch a lot of them or you’d have to scour the feeds to find one that actually sets out to explain the system. Maybe that’s easier than I think; I’ve never looked because thus far, it’s not something I’ve needed to do. Perhaps the next time I decide to run a game that I’m not all that familiar with, I’ll look up some actual plays/livestreams of the system and see if I can answer that question for myself.
I still don’t think I’m going to enjoy watching other people play a game as much as many other people do, though. It’s just not my jam.