What is "decoupling from IRC" in NYS Tax 2020 line 19a

NYS Tax 2020 Line 19a says "Recomputed federal adjusted gross income" (see page 16 line 19a worksheet)

I go to the worksheet and it says

Line 19a – Recomputed federal adjusted gross income
Were you required to report any adjustments on Form IT-558?
If No, enter the line 19 amount on line 19a.
If Yes, complete the worksheet below.
Do not leave line 19a blank.

I am googling "decoupling from IRC" and it seems that this is due to coronavirus aid.

But I do not understand. Does this mean that coronavirus aid will reduce or increase how much Federal tax you are paying

Who is required to decouple from the IRC, i.e. file form IT-558