While IRS was updating Pub 970 they forgot how they had updated Pub 590-A:

Certain taxable non-tuition fellowship and stipend payments. For tax years beginning after 2019, certain taxable non-tuition fellowship and stipend payments are treated as compensation for the purpose of IRA contributions. Compensation will include any amount included in your gross income and paid to aid in your pursuit of graduate or postdoctoral study.

That's why they call it guidance.  It involves some guys at IRS who dance around trying to keep up with legislation.