Thank you for your post and I apologize for the delayed response!
To hopefully help troubleshoot your issue of finding an app registration in MS Entra ID (Azure AD), I'll add onto the steps shared by @Carlos Solis Salazar .
If you aren't able to find the app within the App Registration section of the portal, please ensure that you don't have any filters set and you can try looking into the other tabs -
Within your Enterprise Applications section, please make sure that you are filtering for All Applications since the default is Enterprise Applications and this could also be causing you not to see your app.
I hope this helps!
If you have any other questions, please let me know. Thank you for your time and patience throughout this issue.
If the information helped address your question, please Accept the answer. This will help us and also improve searchability for others in the community who might be researching similar information.