iMazing cannot extract apps from the iPhone. It just reads what apps you have installed and then downloads them from Apple's servers if they're still available.
There is a similar thread on this topic from last year.
You need to check your purchase history. An app can be removed from the App Store, but still be available to download through your purchase history. If it's not available through your purchase history, then you are pretty much out of luck. Your next option would be to see if you have the .ipa files already downloaded somewhere from when older versions of iTunes used to download the apps to your library (or from iMazing if you have used this app in the past). If you have the .ipa files, you can install them using iMazing.