I am trying to make Google OAuth 2 authentication work with a toy app I am running on my computer (at localhost:8080) using Social Auth for Java.
Howeve
It's actually easier than you think, unfortunately, it took me a couple of hours to figure it out.
Normally when you add multiple links to something on Google or elsewhere you separate it by , or ; but with Redirect URIs you have to use a new line, it's actually not very intuitive. So when you press the Edit Settings button, you can add to the URI and/or Origins if you have a couple more links, separated by newlines (enter).
No need for complicated app configurations or new keys.

On your second question: You have to go to the "Consent Screen" tab to change your app info such as your PRODUCT NAME, HOMEPAGE, LOGO, etc.