Great to have you in the community. The total Qualified Business Income is reduced by these amounts based on Section 199A Regs.  This information can be found beginning on page 43, in the section for '5. Treatment of Other Deductions'.

Yes, both the self employed health insurance dedcution and the 1/2 of SE taxes reduce the income that qualifies for QBI.

You should see that happening on the very bottom of Sch C under the QBI checkbox.

Your income has already been reduced by these amounts, so they dont let you get a deduction again for them.