macOS 'The application can't be opened' — real fix

When You See This Error

You double-click an app — maybe something you downloaded from a developer's site, a cracked tool, or even a legitimate DMG from a small vendor. Instead of launching, you get a dialog: 'The application can't be opened.' Sometimes it adds '...because it is not supported on this architecture' or '...because it may be damaged or incomplete.'

This happens most often with apps downloaded from outside the Mac App Store, apps copied from another Mac, or old PPC apps on Apple Silicon Macs. I've seen it on everything from macOS Catalina through Sonoma. Same root cause every time.

Root Cause

macOS has this thing called Gatekeeper. Every file you download gets a quarantine flag — it's an extended attribute called com.apple.quarantine. When you try to open an app with that flag, Gatekeeper checks it against Apple's notarization service. If the app isn't notarized, or if it's from an unidentified developer, macOS throws that error. Simple as that.

The other common cause: the app is 32-bit (Intel PPC) and you're on a modern Mac that only runs 64-bit. Apple dropped 32-bit support in macOS Catalina (10.15). If it's an old app, that's your problem.

Third cause — permissions. The app's executable doesn't have execute permission. Happens when you copy apps from a Time Machine backup or drag them from a disk image wrong.

The Fix — Step by Step

1. Check if it's a 32-bit app. Open About This Mac → System Report → Applications. Find your app. Under '64-bit (Intel)', if it says 'No', the app is 32-bit. It won't run on anything above Mojave. Period. Find an alternative or virtualize an older macOS.
2. Remove the quarantine flag. Open Terminal. Replace /path/to/App.app with your app's actual path (you can drag the app into Terminal to fill the path):

   xattr -d com.apple.quarantine /path/to/App.app

   If you get 'No such xattr', the flag isn't there — move to step 3.
3. Force Gatekeeper to allow it. Open System Settings → Privacy & Security. Scroll down to the 'Security' section. If you see a message like '“App” was blocked from opening because it is not from an identified developer', click Open Anyway. You'll get a confirmation dialog. Click Open again.
4. Fix permissions. In Terminal:

   chmod +x /path/to/App.app/Contents/MacOS/*

   This gives execute permission to every binary inside the app bundle.
5. Reset Launch Services database. This clears any cached info about the app. In Terminal:

   /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -r -domain local -domain system -domain user

   Then log out and log back in.

If It Still Fails

Check the app's signature. Run this in Terminal:

codesign -dvvv /path/to/App.app

Also check Console.app for crash logs. Open Console, search for the app's name, look for 'terminating with uncaught exception' or 'SIGABRT'. That points to a bug in the app, not a macOS restriction.

Last resort: right-click the app and select Open from the context menu. Sometimes that bypasses Gatekeeper when double-clicking doesn't.

If none of this works, the app is broken or incompatible. Find a newer version or an alternative.