I was running into this problem on the 2023 Home and Business desktop app. In "step-by-step mode" I was just stuck in a loop of the system not allowing me to edit anything. So I clicked "Forms" in the top right of the screen to enter Forms Mode. You can manually make the entries in Schedule A, and then TurboTax will correctly calculate everything. You can go back to "step-by-step" mode to see your changes there as well.
Definitely a software glitch, but you can get around it!
