Is being interesting a compliment ?

I'd say that's a compliment in it's best form like it's been mentioned. Depends on the individual. If I tell someone I find them interesting, it's because I really would like to continue talking with them and want to let them know without sounding like a creep. 🤷‍♂️ Just me though.

That’s what I get a lot. Different people mean different things by it. It’s kind of a compliment but doesn’t really feel like it

Imagine yourself saying that to a guy.

What would you have to feel inorder for you to say that?

It means he finds her interesting. If he does, he'll try to find out more.

He's after an egg that can't be bought in a supermarket?

Depends on what you were doing at the time he found you interesting ...

Trying to keep a slow conversation going

That would depend on the context.

You bet!

It means you have something he likes about you