We were unable to build 5.12.0 without setting the minimum deployment OS to 10.12

The problem is that we have thousands of customers that are still running macOS 10.9, 10.10 and 10.11. They will not be able to upgrade after we move to the new Long Term Support release.

This severely reduces the number of users of our apps, particularly for the education market. Some may be forced to move to competitors.

This would also limit the deployment for Open Source apps as well by dropping support for for individuals, organizations and schools that must stay on one of the previous MacOS releases, either because their older Macs do not support the newer OS or there are other required applications that are restricted to a particular OS.

Standard practice for Mac is to develop for the oldest OS possible, and use weak linking and and runtime testing techniques to determine whether or not newer APIs are available to use on a particular OS, then either skip the new feature or provide an alternate implementation.

Granted, this takes some effort to accomplish.

That being said, the Windows build of 5.12.0 still runs nicely on Window 7. There are many runtime tests that are used to keep Qt working for Windows 7 and still support newer Windows features added for Windows 8 and Windows 10. Windows 7 was introduced in July 2009. 

What would it take to at least support deployment to macOS 10.9, released Oct. 2013? What about 10.10, released Oct. 2014, or 10.11, released 2015? Clearly the earlier the better for our products and for many Open Source projects as well.

CC: atreat, andysh