Why is 2021 state income tax refund received in 2023 taxable on 2023 federal return even though I always take the standard deduction

During 2023, I received a state income refund for 2022 return and for 2021 return. I took the federal standard deduction in 2021, 2022 and 2023. Why is turbotax including my 2021 state refund as taxable on my federal return?