What separates a modern frigate from a corvette?

Should the proposed new US frigate be called a corvette?

No. The practical distinction is operating radius: a frigate is built for distant deployment, while a corvette works near its own shores and region.

The practical distinction offered here is where the ship can operate. A frigate supports distant deployments off another country's shores. A corvette is designed for operations near its own coast and within its region. On that basis, the proposed US ship remains a frigate.