NOTE: prior to 2020 the state tax was in boxes 12-14, 2020 renumbered those boxes to 14-16.
Box 16 is not usually required because it has been an 1099-R industrial standard for many years that if there is only one state in box 14 & 15 then the box 1 amount does not need to be allocated between two states - the entire box 1 amount is understood to be the state distribution so box 16 is just left blank.
But recently, there are at least two states (one being NY) that will reject 1099-R's with a state tax and a blank box 16 so it is okay to enter the box 1 amount into box 16 to satisfy the states requirement.