Deductions & credits

from my understanding, if you take advantage of the deferral,  it becomes very 'kludgy' how you actually pay these amounts by 12/31/21 and 12/31/22.  It's can't be on year's tax return year (note it has to be paid by 12/31 and not by 4/15) so it appears it has to be paid directly to the IRS?????