Apple requiring software to be notarized

[camsr]

Does macOS have anything like Windows' group policy that would forbid any unsigned application from being run?

[beely]

Globally, that's the job of Gatekeeper.

https://en.wikipedia.org/wiki/Gatekeeper_(macOS)

Configuration
In the security & privacy panel of System Preferences, the user has three options:

Mac App Store
Allows only applications downloaded from the Mac App Store to be launched.

Mac App Store and identified developers
Allows applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched. This is the default setting since Mountain Lion.

Anywhere
Allows all applications to be launched. This effectively turns Gatekeeper off. This is the default setting in Lion. In macOS Sierra, this option is hidden by default.[8][9]

The command-line utility spctl provides granular controls, such as custom rules and individual or blanket permissions, as well as an option to turn Gatekeeper off.[6]

But there isn't a way to forbid a specific application to run, if that's what you mean. I suspect this is partly what led to the Notarisation feature...