OAuth2 and JWT can be used together because each one solves a different problem when we are speaking about Security.

If you want to manage what kind of grants and roles your users are going to be part then I think OAuth2 could help you. OAuth2 provides many ways to manage grants and roles.

If you want to give access for other applications then again OAuth2 is going to be right option for you. You can manage that kind of access using OAuth2 and know which applications are using your resources.

If you want to have a Token Based Authentication where you can control validating and know what user is using your API then JWT for sure can be a solution for what you need.