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Due to security reasons, Apple unwilling to use a third party app or unauthorized developers app install on OS X System. Means not available or added on App store by apple. But on Mac users requirements apple allow that after the single alert. Now if you are ready to install and use on your Mac then it’s possible. Look below guide on how to install and Open apps from an unauthorized developer on Mac when you get a message in a popup. show below screen.
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Note: this option available on most of the OS X from Catalina, EI Capitan, Yosemite, or older version as well. 
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Steps: Resolve Open apps from an Unauthorized Developer on MacOS
Now you can short out this through two different ways: Made changes in the system to allow third-party applications for all time. And the second, temporary run app by allowing conditions.
Fix: install The App That’s Showing Unauthorized Developer
Step 1: Open Finder’s Application folder and right-click on install app icon.
Step 2: Next, click on “Open” from dropdown options. (See in below image) 
So you can launch or install any third-party app on your Mac. Now you are able to open this installed app normally from the launchpad.
Best of luck and enjoy it.
Allow to Install all Third-Party Apps on Your MacBook, Mac By Default
For all time you can change settings for all apps from an unauthorized developer message. Under the system, the preferred security option allows skipping this notification. Let’s check how to apply on MacOS X (Also works on all MacOS Version).
- Step 1: Click on Apple Logo () From Top Mac Menu. Next, System preference.
Mac System Preferences Option - Step 2: Then, Security and Privacy > General tab.
Step 4: Now, Unlock lock for make changes in settings. (For that you must required username and password for current users log in) 
Select anywhere. So your Mac never asks for install third party applications in the future. 
Then directly launch the app by double click on the setup icon.
Now you are done. want more help on Open apps from an unauthorized developer on Mac, MacBook, MacBook Pro? We are here for help! So comment on comment section or on Facebook, google+.
Jaysukh Patel is the founder of howtoisolve. Also self Professional Developer, Techno lover mainly for iPhone, iPad, iPod Touch and iOS, Jaysukh is one of responsible person in his family.
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