I'm going to state an unpopular opinion. Bluesky should have ads, not a personalized ads that track users, but just simple ones at the very top of the feed. Consumers today are too addicted to free services, and companies need to be financially independent so that they can support a quality product.
If you mean somebody, somewhere is footing the bill, then sure, if you torture the definition of "free" enough, then nothing on Earth is free. It is worth pointing out that if you enjoy (for example) Wikipedia, then you should donate if you can, because Wikipedia runs on donations. If you're just trying to be a pedantic jackass, though, that's another thing.