When macOS says the game is damaged

It usually is not damaged. The message shows up when a build was downloaded and macOS has not been introduced to it yet. Here is the order I use on the club iMac, the slow way, on purpose.

The message

It says the app is damaged and should be moved to the Trash. Do not move it to the Trash yet. Eject the disk image if it is still on the desktop. A game launched from the image will misbehave even when the file is fine, and the message is an easy thing to blame.

Move it into Applications

Drag the app into the Applications folder. If a copy is already there from an older build, let the old one stay until the new one has opened once. I do this on a weekend, not with the club watching. Two copies is untidy for an afternoon and safer than a Thursday with nothing that launches.

Open it the slow way

1. In Finder, open Applications.
2. Right-click the game, or control-click it.
3. Choose Open, then Open again on the dialog.
4. Wait. The first launch is allowed to think.

That second Open is the step people skip. A normal double-click will show the same warning again. The right-click path is the one that asks a different question.

If it still refuses

The quarantine flag is sometimes still attached. I open Terminal, and I only do this for a build I just put in Applications myself:

xattr -d com.apple.quarantine /Applications/Mini\ Metro.app

Change the name to the app you actually have. Then try the right-click Open once more. If Terminal says the attribute is not there, stop. Deleting random attributes is how a small problem becomes a strange one.

What I do not do

I do not turn off Gatekeeper for the whole Mac so one game will launch. The club computer is used by other people on other days. I do not download a "fixer" that promises to repair the damage. The message is a flag, not a broken file, and a fixer app is a new thing I would have to explain.

If none of this works, I download the build again from the button on the game's page and I start over. A second copy from the same page is dull. It is also the thing that has fixed it, the few times the first file really was incomplete.