Questions

The ones that come up every time.

Is this copyright?

No. Copyright is a legal right you already have. A registration is evidence of when you had it and what it covers.

What if someone registers my work first?

The registry records claims, and claims can be disputed. The earlier, independent evidence you hold is what a dispute turns on. Registering early is how you hold it.

Does registration stop AI training?

No. It makes the use traceable and the bill calculable.