We had a main mortgage loan for the house, and a second mortgage as well. None of the money from the second mortgage was used for home improvements.
The interest paid on the 2nd loan is flat out not deductible.
In 2020 we refinanced and rolled both loans into the refinance loan so that we now have a single loan for the house.
So the percentage of the interest that is equal to the percentage of money used to pay off the "ORIGINAL" loan, is all you can claim as an itemized deduction on the SCH A.
If the new loan is $100,000 and the "ORIGINAL" loan balance at the time of the refi was $60,000, then you used 60% of the new loan to pay off the original loan. Therefore, only 60% of the interest is deductible on the SCH A every year, for the life of the loan.
