Jack's iMac runs El Capitan, and his iMovie and Garage Band have stopped working. He has been told he has to upgrade to get them working back. But he's hesitant. Leo says that it's OK and you should upgrade. Apple isn't like Windows. You can safely go to Mojave, or at least High Sierra. Why did your apps stop working? That's a puzzle. Maybe your graphics card is too old? Or Apple may have just broken the connectivity. Upgrading to Mojave though is important for security reasons.