IssueProbable Cause
Issue
To install a WordPress plugin, you need a zip file, which is how we provide Gravity Forms and Gravity Forms add-ons upon download. But what if your download is not a zip file?
Probable Cause
This likely means you that your browser is automatically opening (unzipping) the file at the time of download. This is a user preference within your browser settings.
For example, in Safari:
Open Safari >Preferences >General
Uncheck 「Open Safe Files After Downloading」
Re-download the file.
Screenshot shows Safari Preferences panel, as of Safari 14.0