People always confuse multiple things.

There is gravity, the actual effect we see every day all around us. Gravity is a real thing, it exists. Then there's the law of gravity, this is a math formula you can use to predict the effect gravity has on things. There's multiple variations of this one, think Newton and Einstein. For almost everything the Newton version works just fine. Then there's the theory of gravity, this is our attempt to explain why gravity exists and why it does the things it does. This is the tricky one we don't really have a grip on.

By mixing these things it is often portrayed that "scientists" don't know anything, they don't even understand something as simple as gravity.

In a way. I mean we know it exists, no one would reasonable deny it, but the exact mechanism are still debated. How much is beneficial adaptation, how much is genetic drift for example. But the common ancestry is as common sense as that an apple will fall to earth

I audited a class on the topic. The professor said something like, "Some folks think evolution isn't a fact, it's just a theory

but they have it backwards! It is a fact...but it's a lousy theory."

That was great. :)