You have to read the final regulations (link below) which are somewhat obtuse and involved.
Regardless, there is really no way to enter the figure from 11A in an online version of TurboTax as per the instructions you mentioned in your post. Rather, you would need to use a desktop version of TurboTax for that purpose.
https://www.govinfo.gov/content/pkg/FR-2020-10-19/pdf/2020-21162.pdf
