I'm not a Mac user, but let's see if I can get you going.
When you see the '"CHIRP" cannot be opened because the developer cannot be verified' message, I believe this appears because the CHIRP project does not pay Apple to get CHIRP "notarized". Apple wants you to be sure that you really want this "unknown" application to be run on your computer. You will have to go through the process of telling macOS that you do want CHIRP to be allowed to run on your computer. Click the [Cancel] button to do this.
Next you need to open 'System Preferences' and then launch the 'Security & Privacy' application.
In the 'Security & Privacy' application with the [General] tab selected, you should see '"CHIRP" was blocked from use because it is not from an identified developer.' in the lower half of the window. Click the [Open Anyway] button.
Now you should see a 'macOS cannot verify the developer of "CHIRP". Are you sure you want to open it?' message. Click the [Open] button.
CHIRP should now run for you.
Remember how to do this because you will have to repeat the process following any future CHIRP updates that you download and apply.
Jim KC9HI