Sources

PONG assets: 

https://myebstudios.itch.io/simple-ping-pong-assets

Questions I asked ChatGPT:

How do I make the pong ball bounce in Unity?

unity 2d destroy if offscreen

unity 2d respawn when destroyed

I didn't end up using all of these things, however. 

I also used this YouTube video to assist me with some scripts: