HI there, I read many posts about X-Plane 11 and graphic problems with MAC OS-High Sierra. Unfortunately I never saw a solution. My specs are IMAC late 2013 with 32GB Ram, Nvidia Geforce GTX 780M 4 GB and a 500GB SSD-Drive.
The moment I updated to High Sierra, X-Plane was not "flyable". I downloaded the latest Nvidia Drivers, deleted all preferences and also did a ???-Ram-delet (with cmd function R P). Whenever I start X-Plane, all seems ok untill 5 to 10 min. after take off, framerate drops from about 35 to 1 or 2 or 5 or 0.4... not flyable from this point of time. 11.05r2 seems to be a little bit better than the 11.10b releases.
As far as today I never read any more solutions than the mentionned above. Hopefully there is more out there, otherwise X-Plane is not flyable for me any more.
Thanks and sorry for my english, which is not my native language.