I wouldn't cite him as a YouTuber first, but Jeff Nippard is a a reputable source. He's competed and won in natural bodybuilding competitions, set powerlifting records for his province, partnered with PhDs in the field for studies on hypertrophy (and is one of the people leading the charge on 'lengthened partials' as being one of the most efficient ways to build muscle, which the research does agree with.)

But yes, he is also popular on youtube.

He seems like a reputable guy, and everything you mentioned is all probably best case scenario for someone who's not in a regulated profession or who's job it is to produce credible research. I'm not disputing that or him or any of his records (though incidentally it seems like his 1st place wins were in provinces with the fewest people), and I tend to enjoy his content. He also seems to have a bachelor's in biochem, also great, I don't.

I also like a bunch of other channels and have derived what feels like good information from them, I'd recommend them on that basis to people I felt would find it useful or entertaining. Just because I wouldn't cite them as an authoritative source doesn't mean it's a strike against them, it just means I don't think it's fair to tell someone they're wrong because my favorite YouTuber, even if they seem credible, well-natured, and are worth recommending, says X.

There are plenty out there doing good by their viewers and I love that, especially Canadian ones, but it's insufficient for being hyperbolic, imo, about what's impossible to make a claim about, and I don't think arguments from apparent authority are to be encouraged anyway.

In some cases, I've checked the advice of other MD content producers against real practitioners, and they've gave me the thumbs up in terms of credibility, and that obviously changes the vibe a bit, but still I'd hesitate to go too far with that, there's a lot people will do for money and attention.