We can't see your tax return so don't know if there would be something else affected by not making the DCFSA contribution that would increase your income taxes. For example, what if that extra $5K in taxable income pushed that income into the next tax bracket which is 22%. Thus you would really be saving $1100 in income taxes + the $200 remaining DCC = $1300 but only get $1200 DCC so not making it would cost you $100.
however, that $5K also affects the Child Tax Credit and Earned Income credits and maybe other items as well. So it's difficult to know for sure if worth contributing to the DCFSA unless you do two returns one with everything and then the second eliminating the $5K from box 10 and increasing box 1 by $5K on your w-2.
Taxable Medicare and Social Security wages? Not sure but I believe the $5K reduces these wages and thus these taxes that you pay if you did not make the DCFSA contribution on the $5K so if I'm right that's a savings of $5K times 7.65% or $382.50
Nothing can be done for 2023.
