A plugin can be blocked on your Mac for two reasons. First, it may not run if it’s out of date and lacks functionality to fully support your current software. The other scenario kicks in when Apple prevents a specific plugin from being executed due to compatibility issues or security concerns. The latter situation is far more common, given the Mac maker’s hardening control over the ecosystem of third-party code. If a plugin – which is technically a piece of software – fails to pass macOS notarization checks, you won’t be able to launch it and view web content that uses this potentially harmful entity.