For iOS 15.3.1, iPadOS 15 Easy Walkthrough Steps for Apps Stuck on iPhone and Showing Loading, Updating, Waiting to install or Download new Update after update button in app store. Apps Taking too much time on installing, Updating on the home screen. With Label named Waiting, Loading, Updating on iPhone 11 pro max, iPhone XS Max, iPhone XS, iPhone X, iPhone 8 or Other Model.
Source: https://www.howtoisolve.com/apps-wont-download-install-update-ios-iphone/
Easy Troubleshooting solutions for the issues on iOS 14 won't install or Stuck on Downloading, Updating, Installing.

soln 1: Check the Internet connection
soln 2: Multiple Apps are Updating or Downloading at Once
soln 3: Sign out and Sign in App Store or iTunes Store
soln 4: Set Date and Time to Automatically
soln 5: Hard Restart/Reboot your iPhone
soln 6: Delete Stuck app and Re-Download
soln 7: Reset Network Settings/Reset All Settings
soln 8: Force Close App on iPhone
soln 9: Check For Software Update

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https://www.youtube.com/watch?v=ZyqRNvblzLg

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