I’d enter it as two lines - one for net 25.32 at 20% VAT and one for net 198.27 at 0% VAT. But you could just enter one line with net of 223.59 (= 198.27 + 25.32) and manually edit the VAT column to say 5.06. On the purchase side QuickFile’s own calculation of the VAT as a percentage of the net is a convenient starting point, but you’re always free to edit the VAT value if the calculation is wrong - for purchases the only thing that matters is that the total net and VAT amounts that you record in QuickFile exactly match the total amounts your supplier charged on their invoice.
It’s the supplier’s invoice that tells you how much VAT you were charged, and therefore how much you are entitled to claim back.