Can I access Azure AD resources, like the name of the apps and other details without registering a new app? I would like to query the REST APIs.
No, you can't. The only REST API for Azure AD is the Graph API. And you have to register an app to use. The Azure AD PowerShell Module itself has a registered application.
You simply cannot get a token without registering an application. Azure Portal itself is also a registered application.
In the OAuth World (explained here) you have the very important part - client, which is the registered application in question. You cannot avoid it.