The information above is simply not correct. I can attest to that as a professional MacOS software developer.
The choice to tie the software to a specific MacOS version is entirely in the hands of Intuit.
To add to this I have been using TurboTax for over 10 years (current system contains returns since 2011). I am currently on MacOS 10.14 and will not upgrade (for a variety of valid technical reasons, that are well beyond this discussion). This year, in anticipation of not being able to use TurboTax in 2021, I purchased HR Block software and ran it along TurboTax.
The resulting returns are essentially identical (HR software wins "by a nose" in the amount of the return). Crucially, HR software does not choose to be tied to the most recent MacOS, so I should be good with it for quite a few years to come.
It is unfortunate that Intuit decided to take the way of "version treadmill". Now you lost my business - little though it may be.
