The major change in recent Mac OS is that it removed "Run App From Anywhere" in the settings. myTaxExpress and T2Express software are not listed in App Store. You need to do the following to run the software.
1. After you download myTaxExpress/T2Express Mac version, you need to move it to Applications folder.
2. Keep holding down Ctrl key, and right click mouse on myTaxExpress/T2Express inside Applications folder, then select Open, confirm to run myTaxExpress/T2Express app.