A fair chunk of them do it by selling the supposed secrets of making scads of money online! Some 'influencers' make good money but it's more than a few hours a day if you include all the hustling, showing up to events and/or travelling, and ensuring an Insta-ready lifestyle.
People used to make passive income by running aggregator websites - second-hand content stuffed with keywords, with the money coming from advertisements. Those are mostly owned by large groups now, using AI to write the stuffed copy.
If you have niche skills or specialised knowledge, you can try starting something up in your spare time (you'll have to make some!) and learning until it's grown sufficiently to replace your income.
Some possibilities:
If you're great at SEO or prepared to learn, start a website on a topic you know well. Make a YouTube channel, Instagram, Twitter, TikTok and whatever comes next. Sell ads.
Gaming: A handful of people make incredible money playing games. They profit in-game, offer paid access to recordings of their play, sell cheats and hire themselves out to play for other people.
Gambling: Professional gamblers do exist. Not recommended.
Sex: Make videos of yourself being 'sexy' on Only Fans, run associated channels on all the other platforms. The money comes from one-to-one interactions with weird blokes: prostitution at one remove. Best if you've got a specialism.
Freelance professional skill: Could be anything from accounting to design. Start a website as above, offering your service for hire, and ensure you're present on all the related platforms.
Invent a platform: If you've got a new idea that nobody's done yet and could grow like Uber, go for it!
There will be plenty more once you start thinking. I'm pretty sure you'll have to start small, though.