Well, this is not conclusive, but it may not be an IRS limitation.

I made the mistake of buying CCH ProFX, and testing this issue of omitting an EIN for a K1 worksheet does not appear to be a limitation in ProFX.   I think Intuit may be wrong.   See this article by IRS that is two years old now:  National Taxpayer Advocate Annual Report to Congress 2021 (irs.gov)

If it is an Intuit limitation, I wish they would just admit it.