Like other people have said, it does mostly come downto your personal definition of what it means to know a language. A lot of the polyglots I've seen online know a limited amount, but they usually have the accent down really well.

There are genuine exceptions though, where they do have an indepth understanding of the language. That's usually down to personal circumstances as well. And you could cheat a little bit and learn languages that are very similar to one you already know, that can add up quickly.

Not to blow my own horn, but I'll use myself as an example. I grew up bilingual, Frisian and Dutch. As a child I was exposed to a lot of German and then increasingly English, which I both further improved at highschool. During the last two years of highschool and about two years after that, I took an interest in the Scandinavian languages. Then there was a gap for a while, and over the last 3 years or so I've been learning Spanish.

So all in all I'd be quite comfortable having a conversation in Frisian, English, Dutch, German or Spanish. Then if I were to dedicate about 6 months to each, I'd be able to double that list. Norwegian, Swedish and Danish, because I had an interest in them when I was younger, and when you know Frisian, German and English they're not that hard to pick up. East Frisian because it's similar to West Frisian and German. Afrikaans because it's very similar to Dutch.

That adds up to 10 languages. Then if you do start counting like a lot of 'polyglots' do and include the languages where I'd just be able to sit in a restaurant and order a cup of coffee and comment how pleasant the weather is? add a few months for each language and sure, I can start doing youtube videos about how I know 20 languages. would I really though? no.