If you’re confused by how OAuth 2.0 and OpenID Connect (OIDC) work together, please see What the Heck is OAuth? In short, OIDC is a thin layer on top of OAuth 2.0 that adds identity.
The Java world has been very busy lately, especially with all the major Java versions releasing every six months. This honestly can be a lot to keep up with. I was using Java 8 until I was introduced to Spring Boot 2.1.