With respect to the Line 12b issue, I stumbled upon a different thread last night that solved that issue. If you're taking the standard deduction (and NOT itemized deductions) this will apply. Delete all the charitable donation info stored in the usual place in deductions. Go through the screens until you get to Done with Deductions. After that, when the app tells you that you're getting he standard deduction, another prompt will appear that allows (under the CARES Act) a deduction of up to $300 (or $600 married filing jointly) for cash donations. Entering the amount here solved the issue I had with Line 12b. I'm not sure how we were just supposed to know that - at least I found it to be very unclear.
The e-filing issue did not go away, however, so that is definitely a separate issue. I submitted a separate question on that.
