Evidentially TurboTax has chosen to make all the schedules not overrideable for 2020 - I cannot do it either.
Whether this is deliberate or a bug, I do not know. You can complain to customer support if you want but I am sure they will just tell you that data entry on the forms mode is not supported.
There is no single published number because it changes contently depending on the nature of the call and agent availability. Following the link below will either give a current number for you to call or take your number for a callback.
(Note that phone support is for paying customers only. There is no phone support for Free Customers.)
Here is a TurboTax FAQ for contacting customer support.
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
