TurboTax quit supporting 4029 SS Exemption a year or two ago. I had to switch to H&R Block Online after 15+ years of filing with TurboTax. H&R Online isn't as nice as TurboTax Online overall, but supports this tax exemption just fine.
Here is an official answer from TurboTax: https://ttlc.intuit.com/community/taxes/discussion/self-employment-tax-exemption-form-4029/00/327788
