Huh? Lines 12-16 is for the Tax calculated on your income, not the withholding.
Line 19 is the total of line 17 withholding (from W2 box 2 and 1099 box 4) and line 18 for other payments and credits like the EIC.
On the 2019 Form 1040, lines 12a, 12b, 14, and 16 are not tax withheld. They are the total tax that you have to pay for the year.
Line 19 is tax that was withheld from your income, on line 17, plus other payments and refundable credits on lines 18a, 18b, 18c, and 18d. On line 20 or 23, the total payments on line 19 is applied against the total tax on line 16. If you paid more than your total tax (line 19 is more than line 16), then you have a refund on line 20. If you paid less than your total tax (line 19 is less than line 16), then you have an additional payment due on line 23.