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I am not with Laminar Research; just a flight simmer using a Windows based system
Firstly, there are a few flight simmers having success with a Mac and High Sierra but there are also a few having problems. In your original question click on the orange High Sierra tag. It will shown a number of links where others using a Mac system have had a problem.
Secondly, you have not indicated what type of Mac system you have running the High Sierra operating system. You need to have a screen size in the order of 17 inches to be able to get a good image size and good cooling as X-Plane is very resource hungry and generates a lot of heat.
Thirdly, have a look at the system requirements to run the current version of X-Plane. The link can be found at https://www.x-plane.com/kb/x-plane-11-system-requirements/ Many serious flight simmers build a purpose built unit with specifications equal to or better than the recommended system requirements. If you do build a new unit utilise an Intel CPU and a NVidia GPU for best performance. In the early stages of X-Plane 11 being released High Sierra systems were having troubles. Although X-Plane is developed on Mac's Laminar Research staff have been known to suggest in this forum to use a windows based system for best results. A purpose built system will also allow you to upgrade components as and when needed or you can afford to do so
Finally, download and try the free demo version of X-Plane. The demo version can be found at https://www.x-plane.com/desktop/try-it/ Although it is the full version download it will default to the demo version because you won't have the activation key. You will be limited to a fixed airport and a time period of 10 minutes.
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