Amending 2021 return, changing the apply refund to next year amount does not change the amount of tax due when amount applied to next year is increased or decreased

I amended a filed tax return to add a 1099r.

I had originally filed to have approximately $2k applied to next years taxes. After adding the 1099 I have a balance of $5200.

When I changed the $2k for next years taxes to zero it had no effect on federal tax due. It didn’t matter what number I entered for apply to next years return it didn't change anything.