My MAC says it can't open an app from an“ unidentified developer ” ???

Hi lightnin,
This warning comes up on macOS and is expected. Here is Apple's guide on installing software from an unidentifier developer:
https://support.apple.com/guide/mac-help/open-a-mac-app-from-an-unidentified-developer-mh40616/mac

jammr might be available in the App Store in the future, but for now, please follow this guide.

Thanks , Ill give it a try .