I'm not sure achievements will work if the overlay doesn't appear. I can't help much since I don't have a Mac or the Steam version, but hopefully another Steam on Mac player here will be able to help. Can you try running the game through Steam again, then post your latest error log? That's a known issue for some Linux players, but we need more information to figure out why it happens. You can disable SMAPI's update check by editing the StardewModdingAPI.config.json file. (That won't affect individual mods that check for updates; SMAPI doesn't provide an update service for mods yet, so those mods have their own code to do it.) Does disabling it affect the launch issue? A MissingMethodException normally means you have an older version of .NET Framework. Try installing the latest version of .NET Framework.