The IRS has changed the 1099-NEC printed form to a 3-up copy. For the Recipient or Payer/State Copies, only the 3-part perforated paper will be accepted – the 2-part perforated paper used in 2020 (or prior) will no longer be accepted.
You can order the 3-part perforated paper from Nelco. Their contact information is 800-266-4669 or Nelco Solutions.