What won’t run? ON YOUR MAC,
Some of our apps are missing…
unlike iOS devices, you can run software that hasn’t been vetted by Apple. But that doesn’t mean macOS won’t try to protect you from yourself, and Catalina gets noticeably tougher. You’ll already have experienced how Gatekeeper stops you running an app that isn’t from the Mac App Store until you confirm. In System Prefs > Security & Privacy, you can still opt either to allow only apps from the App Store or those from “identified developers” too. But Gatekeeper will now scan apps for malware, and it’ll repeat this, as well as its check on the developer’s digital signature, from time to time. So you may experience delays and occasional rejections.
There’s one category of apps that, for the first time, you can’t run at all under Catalina. As we were warned, Apple has ended support for 32–bit apps, written for processor chips that haven’t been used in new Macs since 2011. You should already have seen “not optimized for your Mac” alerts pop up when running these apps, but to confirm which (if any) are affected, Alt–click the Apple menu and choose System Info, click Applications (under Software on the left), wait for a list to appear, then scroll to the right and click to order it by “64-bit (Intel)”. Apps that say “No” aren’t ready for Catalina, so you’ll need to see if new versions are available.
NO UPGRADE, NO INSTALL
Some Adobe Creative Suite apps were still 32–bit up to CS5 or 6, so if you don’t want to upgrade them, then make sure you don’t install Catalina. Apple’s iWork ’09 apps were 32–bit; if you’re still using them in preference to the current versions, you’ll have to decide between a free upgrade (from the Mac App Store) or putting off upgrading macOS. Aperture, the Lightroom rival that Apple discontinued back in 2014, was 64–bit, but won’t run in Catalina, for, er, whatever reason. Apple did update its DVD Player app to 64–bit in Mojave, so this will still run under Catalina on a 2012 MacBook Pro, which is the last compatible model with a DVD drive.