Have been scratching my head with this issue today.

I have tried the two line solution which is fine. Not sure how things were in QB in 2019 but you can log the mileage in the Mileage section so that would cover the normal mileage expense but not the VAT portion of the mileage. However if you create another line in expenses aren't you creating another expense and falsely submitting two expenses. 

I have tried doing the second line but then  "minused" the net value of the expense and put No VAT at the end. This way only the VAT portion counts and not the net expense.