in my experience (25 years). Most platforms are built to support a Windows environment. I do not know of any text expanders for MAC for use with MT.
As an example, the Emdat platform using Internet Explorer to enter text - you don't see IE, what you see is a blank box in which to transcribe, but the platform needs IE to create that window.
Furthermore, most text expanders are built on the old DOS platform and then later updated to work with Windows, not MAC.
A huge component of platforms is the use of MS-Word. An example is that you cannot use a student version of Word when using most platforms because it does not contain the hidden codes a full version needs to hand-shake with your computer. It is also the reason you cannot use a little tablet to do MT work.
I think at this late date, using a MAC would be recreating the wheel and you would find converting to a Windows environment the easiest route into the MT world.