I took some time to search online and there's not much on this topic, making me believe that TurboTax maybe is buggy on this form or something. Don't take my word for it since I'm no tax expert, but I just left it as no entry, even though the "check entry" complains about it.
Here's what I found:
In 2021 year instructions for Schedule K1 Form 1120S, there's no mention of the dropdown options: Pre-1936, historic under trans rule, historic not under trans rule. It also mentions that Box 13 Code E is related to Qualified rehabilitation expenditures (rental real estate). My S Corp is nothing related to rental real estate at all, which makes sense since Box 2 and Box 3 of this schedule are empty since I don't have any real estate income. https://www.irs.gov/pub/irs-pdf/i1120ssk.pdf
In 2004 year instructions for Schedule K1 Form 1120S, that's where the first mention of Pre-1936, and historic that I can find on Line 13C. https://www.irs.gov/pub/irs-prior/i1120s--2004.pdf. This also applies to Rental Real Estate which doesn't seem to apply to me either.
After reading through that, it seems like it doesn't apply to me even though it fails at the check.
