Issue
You named your app example-app and are wondering why the app URL is example-app-1234567890ab.herokuapp.com.
Resolution
On June 14, 2023, Heroku will start appending 12-character random identifiers to subdomains to prevent domains from being taken over after renaming or deleting apps. Any apps created on or after that date contain the random identifier in their subdomains. The URL format is APPNAME-IDENTIFIER.herokuapp.com. The random identifier is not considered to be part of the app name.
See the Dev Center for more info about app names and subdomains.