Discussion on: If I don't use React, am I still a developer?

1. One does not. The vast majority of it is sturm und drang, which will leave yet another smear of legacy code across the landscape.
2. That depends. The fundamentals aren't changing. There's nothing in React or the latest crazes in JavaScript that wasn't already known in the 1970's. There's nothing in the NoSQL or database world that wasn't already known in the 1980's. It's just showing up in a context that didn't have them before. If you have enough fundamentals to learn the local details just in time, then you're fine.
3. There's a place for all kinds of people. Don't worry too much about definitions. One of my neighbors is an advertiser who also runs his own Linux fleet, does some rough machine learning, and handles his own business. Advertising is his core competency, and he's just good enough at the rest to make it work and ask for help if he needs it.
4. It depends how much complexity you're willing to ignore at each layer. If by full stack you mean able to deploy a server, set up and administer the database, write and deploy a backend binary, and write the HTML and JavaScript that it serves, then, yes, it's completely straightforward. Just be aware that each one of those layers can scale into a career in its own right. The problem is knowing what parts you actually need to know and what parts only apply when to problems where you need specialists and their more complicated tools.
5. I have never used React. There isn't a soul on the planet who would think that I'm not a developer.

Being in the remote Upper Peninsula of Michigan, it's difficult to find developers to learn with. I don't relate to a thing I read about the culture of Silicon Valley or the startup scene. Being entirely self-taught I feel basic concepts of programming or development are beyond me.

I grew up in the mountains of western Virginia. I totally get it. This is why the Internet is wonderful.