Or just what they're showing you?

It doesn't remotely do what people in this thread seems to think it does. Which is bizarre given you can go set up an account for free and see for yourself.

They seem to be confusing it with some of the third party ad tracking software. But GA is really dumb as a brick (and that's a feature, not a bug).

The concern isn't about what GA gives to its implementers, it's about what it collects internally.

Google is an advertising company and has a financial incentive to stalk everyone. Their bad faith implementation of the GDPR consent flow (which IMO does not actually comply, but the regulators are incompetent or unwilling to enforce the law) proves it. The current regulatory environment doesn't do enough to discourage non-consensual data collection, so given this fact and the company's past history we need to assume the worst until proven otherwise.