Intuit has a somewhat difficult relationship with Mac. Whenever Apple releases a new SDK (software development kit), Intuit seems to jump right on it. This is good because it gives Intuit the ability to use the latest OS features, but it can be bad for users because Apple routinely removes support for older systems from their new SDKs. For software companies to support older Macs, they have to write multiple versions of their programs or use the old SDK, and Intuit doesn't do that.
So chances are, even now, Turbotax 2017 and earlier won't run on a Mac that is running OS 10.15 (Catalina) or 10.14 (Mojave). And Turbotax 2019 and 2020 won't run on anything older than Mojave.
So on a Mac, it's really important to save your tax file as a PDF (both the tax return version and the all forms and worksheets version) because you can open a PDF anytime without needing a working copy of the tax software itself.
