An unlocked and SIM-free iPhone can be activated with those carriers. I activated mine in seconds.I went back to the Apple store and read the single Asterisked * conditions at the bottom of the iPhone 11 purchasing page, for additional consideration:
"...Monthly pricing: Available to qualified customers and requires 0% APR, 24-month installment loan with Citizens One or Apple Card Monthly Installments and iPhone activation with AT&T, Sprint, T-Mobile, or Verizon. Taxes and shipping not included. Additional Apple Card Monthly Installments terms are in the Customer Agreement. Additional iPhone Payments terms are here. "
/shrug