I already download mcdonald app but it keep saying application initialization critical error occurred. Please restart the app

If it's badly broken, wait a day or so before using it again and try again on the off chance that the McDonald's server is malfunctioning, and—if it's still failing—you'll then want to check with the folks supporting the app for an update.

Or leave a review mentioning your issues in the App Store, as the app developers are responding to posts there.

The developers of the app are the folks that will need to be involved here, if the app is malfunctioning.

Delete the app and then download it again. If the issue persists then contact the developer of the app to address the issue.

Axel F.