After some frustrating time with Microsoft I contacted Apple. The very helpful service person (Asylyn) helped me upgrade to 10.13.6 and Turbo Tax 2019 works well with it. Every other avenue I tired suggested that an upgrade past 10.12 was not possible. Once again, Hooray for Apply and iMac. Not sure what will happen next year if TT puts a barrier to use under 10.13.6, but the idea of using free software or just hiring out the effort will likely be my approach.
