Schedule K-1

I received a Schedule K-1 form and in Box 14 has "I*" and underneath Other Information it has "STM". 

This is the first time I ever received a Schedule K-1 form and I have no idea what all of this means.

What does STM stand for?

In TurboTax, when I enter the letter "I" in Box 14 it turns red as if this entry "I" is incorrect.

The code table indicates the letter "I" stands for "Section 199A information". What does that mean?

Does anyone have suggestions?

Also, I received a "Statement A-QBI Pass-through Entity Reporting" - the only amount on this form is beside "Rental Income". Do I need to enter this information somewhere on TurboTax - if yes where?  

Again, I am new to these forms and information.

Thanks!