I do not believe that ABP has a shortage of documents on this issue. You can use it as follows:
[Authorize(Roles = "admin")]
ABP uses policy-based as you know. Again, as you know, policy-based authorization underneath the covers, role-based authorization and claims-based authorization use a requirement, a requirement handler, and a preconfigured policy. These building blocks support the expression of authorization evaluations in code. The result is a richer, reusable, testable authorization structure.
Also see: https://stackoverflow.com/a/58465136/9922629