It wouldn't be right if 1/2 SE tax deduction is allocated to the QBI from K-1 rental.

Allocation of 1/2 SE tax deduction attributable to the respective qualified trade or business is normally done based on share of each qualified ToB's net earnings on Sch SE.  In this case, the K-1 with only rental income would have no income subject to SE tax.

How is PS allocating the 1/2 SE tax deduction to the QBI from K-1?