Pretty much every "free" app you use today makes money by showing you ads. On the other side of that equation is a person or company who paid for you to see their ad. If you've never set up paid advertising before, I'll tell you it's surprising how accurately you can target your audience.
Google search result ads are pretty straightforward. You search for "X" and whoever paid the most for advertising to "X" searchers gets their ad displayed. But on Facebook, Adwords (by Google), Twitter, etc. advertisers target people instead of search terms.
You can target men aged 29-42 with early school age children who own their own home in the greater Seattle area making a 6 figure income... and that only takes a few clicks. This is possible because these websites have a ton of data on you, and they make their money by selling that data to advertisers.
Thanks to various regulations, you can force these apps not to keep your detailed demographic data, but the result is advertisements that aren't particularly interesting.
Web3 allows you to own your own data, so advertising in this traditional way doesn't work. Brave browser is privacy focused and includes a lot of blockchain functionality out of the box. It's impressive how they're able to make money from advertising without taking your data. (by the way, I'm not being paid to say this) I interviewed Luke Mulks from Brave about their focus on privacy and accessibility on the podcast this week. Enjoy!
P.S. I use Brave and really like it, so if you like privacy, give Brave a try.