You can use Saurik's IPA Installer to recover IPAs from apps installed on the device. To do this, install IPA installer console via Cydia. Then, ssh into the device and look up the bundle id of the target app. For example:
iPhone:~ root# ipainstaller -l
com.apple.Pages
com.example.targetapp
com.google.ios.youtube
com.spotify.client
Generate the IPA file for using the following command:
iPhone:~ root# ipainstaller -b com.example.targetapp -o /tmp/example.ipa
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