I spent a long time on the phone with a TurboTax agent and I don't know why but the reason we were seeing this error is that TT was showing "You are using the Standard Deduction" when in fact, it put me in the itemized deduction. Line 10b should be blank for all people using itemized. If you're having troubles, you should double check which deduction you are using by clicking the box "Change my deduction" on that page. It showed that I was indeed using itemized, so I just cleared out the $300 from that line.
I don't know that everyone is having the same display error as me but it's one possible avenue. The TT agent was super surprised and confirmed multiple times that he saw it say Standard Deduction. At some point, I saved a copy of my tax return with a different name, and it all of a sudden switched to showing Itemized Deduction even though I hadn't changed anything. I hope this helps someone out there.
