The excluded professions for QBI come into play when the taxpayers taxable income (income after all deductions and credits) is above the thresholds of $157,000 single and $315,000 filing joint.  If one's taxable income is below the thresholds, then the exclusion for the Specified Service Trade or Business (SSTB) does not apply.  Therefore, TurboTax will bring up the threshold issue related to SSTB's after all of the income and expense information is entered into TurboTax. 

These are a few of the questions that will be asked once you enter your self-employed business data (income and expenses).  These questions are 1) whether all the income was earned in the United States, 2) whether the income was earned from a previous employer and 3) whether your total taxable income will be above the thresholds (needed if business is an SSTB).  If one answers that they want to work on the threshold question, then the taxpayer will be brought through the questions related to the SSTB's.  See the sample screenshots attached. 

Here is more information on how the Qualified Business Income deduction is calculated:

https://ttlc.intuit.com/replies/7019998