Thank you,
so the trick is to move it outside the Source folder, for example we could put ThirdParty on the same level as Source:
PrivateIncludePaths.AddRange(
new string[] {
"MyPlugin/Private",
"../../MyPlugin/ThirdParty/glm"
}
);
Unfortunatly, this only works when including headers. You can’t add source files to compile this way, because the build system will remove the folder from the project as soon as you call “Generate XCode project”.