Re: "The Mac App Store should allow you to download the latest compatible version for your OS and machine. Is that not happening?"
Unfortunately, all that seems to be available to me is the newest version (3.6.3). I was hoping to discover links to previous versions. My early 2011 MacBook Pro is running Monterey 12.6.2 which is a non-supported OS. Maybe this confuses the process, but apparently getting Monterey to run successfully does not guarantee other apps will seamlessly work with the older hardware. Rather than to revert back to High Sierra just to access MainStage 3 and get it to work again , I prefer staying with the newer OS. Monterey has breathed some new life into an older computer.