The reason you aren't able to efile the return with schedule C included is because of form 7206. Form 7206 isn't set to be available until 2/7/2024. Tax Forms Availability TurboTax
I have the same issue when attempting to efile with my Schedule C, I get an error I have to file by mail. If I delete the Schedule C it will allow me to efile. So I will wait until 2/7 or 2/8 and try again. Hope that helps!
