In Catalina and Big Sur, notarization is no longer a bonus: for some types of software like extensions and most plug-ins, it’s essential. The only two general exceptions are software supplied through Apple’s App Store, and Apple’s own software, including the whole of macOS itself. You can still run apps and command tools which haven’t been notarized, but if they’ve been downloaded from the Internet or moved to your Mac using AirDrop (which also sets a quarantine flag) it’s getting progressively more difficult to do so. In Big Sur, it’s no longer just a matter of opening the unnotarized app in the Finder.
Notarization
When a developer notarizes their software, they have to build it to comply with Apple’s rules, which include signing it fully and correctly, and ‘hardening’ the runtime. They can’t submit the app or command tool as it stands, though: it has to be packaged in a way that’s acceptable to the Notary Service. That includes disk images (in UDIF format), signed flat Installer packages, and Zip archives (as used by Xcode to notarize apps). The notarization is then specific to the app or executable contained within that.
The Notary Service checks the submission for malware. If none is found, signatures are in order, and other requirements are met, Apple adds its cryptographic hash and other details to its notarization database, and issues a ‘ticket’, which the developer can download and ‘staple’ (attach) to the software.
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