I'm running macOS High Sierra 10.13.4 and installed via the Open Installer. Everything went smoothly but when running the wxlauncher and selecting the proper root folder / exe I can not select a resolution and the "Play" button is greyed out. In the lower right corner it also says when first selecting the root folder:
"image255x112 has invalid dimensions 252x111"
And after that
"FS2 Open did not generate a flag file"