A Mac blocks an app from an unidentified developer

A macOS warning is a decision point, not an instruction to find the override button. Gatekeeper checks whether an app from outside the App Store has an identified developer signature, is notarized where required and appears unaltered. A legitimate independent app can trigger a warning, but so can a malicious download. The risk is highest when a page told you to bypass protection before you expected the warning.

Decide before you override​

1. Stop and identify the exact app and installer source. Did you intentionally request it from the developer's official website, or did a search advertisement, email or pop-up send you there? Delete the file if its origin is uncertain.
2. Look for the developer's own installation instructions and compare the product name and download URL. A copied logo or review on an unfamiliar site is not independent evidence.
3. If the publisher is legitimate, ask why this build lacks the expected signature or notarization. Prefer a signed current release from the official source. On a managed Mac, contact IT rather than changing a security setting yourself.
4. Only when you are certain the app is trustworthy and unmodified, follow Apple's specific System Settings → Privacy & Security → Open Anyway procedure after an attempted launch. Do not disable broad protections or run Terminal commands from a stranger to force installation.

A notarized app still deserves judgment​

Apple says notarization checks for known malicious content; it is not a promise that every future behavior is safe. Its safe-opening guidance describes Gatekeeper and the narrow override. Its unknown-developer guidance warns against overriding for an unverified app. If you already ran a suspicious installer, review login items and account activity instead of assuming a later deletion undoes its changes.