It is probably a bit too early to really trust the functionality of the 2020 software. If you are at the input point for those entries, try pressing F1 to get more information.
Try a negative number and see what happens when you try. I have not seen very many WI users on the forum and I don't do WI. My guess by looking at the forms is that the answer is NO. AD is for additions and SB is for subtractions, so I would assume all positive numbers to either ADD or SUBRACT.
Here's wishing you many Happy Returns
I contacted the WI DOR and they said that negative entries are not accepted. However, it is also true that they have not defined the element in their schema as a requiring a Non-Negative number so unless Intuit has added preventative measures, a negative number will pass. I have suggested to WI that they change the schema to not allow a negative number.+