It is foremost to mention that the PMP exam is NOT based on “A Guide to The Project Management Body of Knowledge (PMBOK Guide)" However, this is the main source of reference and study for the exam. Nonetheless, the PMBOK 6th edition remains a valid reference and source of knowledge for the 2021 exam prep. However, you must focus on developing your competencies based on the "Exam Content Outline" for the 2021 Exam, officially created in June 2019.