If your Mac will not support the desktop software then you can ask customer support to do an "exchange" for the online software or at least credit the amount you already paid toward the online software. Online is not the same price as desktop software, so not sure how they will handle that.
To call TurboTax customer support
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number
They are available from 5 a.m. to 5 p.m. Monday - Friday Pacific time.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
