Just a few discussions on this:

https://proconnect.intuit.com/community/forums/searchpage/tab/message?advanced=false&allow_punctuati...

AND... the first installment had to paid by 12/31/21 either using the voucher that came with the letter notifying the client of the obligation, or at irs.gov, or via EFTPS. 

If that first installment wasn't paid by 12/31/21 - the entire deferral became due, with penalties & interest all the way back to 5.15.21 (I think that was the original due date for 2020 returns, right 🙂

The deferral is NOT paid via any addition to the 2021 tax return.