create if not exists:
var libFolder = FileSystem.AppDataDirectory;
var appFolder = Path.Combine(libFolder,"app");
var logFolder = Path.Combine(appFolder,"log");
if (!Directory.Exists(appFolder)) Directory.Create(appFolder);
if (!Directory.Exists(logFolder)) Directory.Create(logFolder);
note: on macOS .net 8 is a catalyst app, and the data folder is the sandbox folder (~/Library/Containers/<appname>/Data). The install will also create links to common folders that the manifest specifies (Downloads, Movie, Pictures, etc).