Are vpns able to keep you private and hidden or can some still be like "we know what you're doing/looking at"?

I have a question. Do you trust anyone selling you something.

il bet those with VPN are monitored the most

The VPN provider can see the same as your internet provider would otherwise. Which is why it's curious how much advertising budget is available to funnel the data from hundreds of internet providers through a few VPN providers. 🧐