From what I've seen, polyglots either:
1 Have a very low bar for fluency so claim to speak a language fluently with a really very basic practical lexicon and often, awful pronunciation. I'm sorry that this is a negative and cynical view, but when I see videos of people bragging about being polyglots, this is usually (not always) the case.
2 Have a lot of time. There's no way around it. To speak several languages at at least an intermediate level, you need time, especially if you're going beyond the languages in the family you speak. Some people add up the time by staying committed to language acquisition for years (becoming genuine polyglots in their thirties or later), some don't need to work and can make language learning a full-time activity.
3 Have a particular talent that makes their performance in languages seem better than it is: maybe they have an ear for sounds and can mimic those well, so they sound native-like even if they have limited vocabulary. Some have an excellent memory and so can impress you by always finding the appropriate word for the situation.
There are a few polyglots I think deserve the title and are genuinely fluent in many languages, but most of them are older, have been learning languages for years, are retired, or some younger ones have found a way to make it their career.