Its due by 12.31.21 and 12 31 22 so no, it wont go on the 2021 or 2022 return.    I havent seen any guidance on how this gets paid back, Im guessing the IRS will send some kind of voucher at some point, ultimately the taxpayer will be responsible to make sure th payment reaches the IRS, but Ive got to guess they will send something at some point.

Another thing to note if the taxpayer has a refund - IRS does not allow the deferral.  

The provision for employers will be that they get billed for it; this provision for SE likely means they also will get billed for it.