I think that's why a lot of people find addiction - to make up for what they don't have.

You're probably correct, although I also think once an addictive pattern is established there's often a kind of feedback loop where the pattern interferes with your ability and options to have a better life.

If you live alone, have no kids or pets, and all you do after work is play video games or doom scroll or watch porn; as long as your bills are being paid, is this an "addiction"?

I guess there's a few ways to answer that question. In an extremely literal sense, no one is ever going to be diagnosed with anything if their behavior doesn't affect themselves or others around them negatively. But if we define addiction as a certain behavioral pattern, this person would still be addicted to their phone given that this behavioral pattern is present. Do they "play video games or doom scroll or watch porn" every day simply because they're bored, or because they can't help themselves? And if an opportunity arose and this person's life had a chance to turn significantly better somehow, would this behavior stand in their way?

I'm not saying I know the answer, by the way, and I'm certainly not judging anyone in this kind of situation.