I did it years ago when I was a teenager with no real job. There were a bunch of higher-paying jobs like lecture transcription that would be a few bucks each. I made enough to buy a GPU off Amazon (~$80, some of which was from a leftover gift card).
Now I'm sure that ML-AI can do those jobs much faster and cheaper, for about the same accuracy.
Many companies are using AI to generate AI training data. Most of them are data brokers where the margins are becoming razor thin. It's totally a bad idea, but it is definitely happening.
Go back a decade and it was a little better. I used some scripts that optimized things, along with the Turkopticon community this article mentions and a subreddit for high paying tasks.