Can I use the June 2020 study material for December 2020 exams?
Yes i think you can use that. I am using 2017 PM book to give exam in the coming sep 2020. The syllabus for this course has been same from many years but changed slightly in terms of techonological topic updated due to covid-19.
Also the they have provided the change made in the technical articles of this course which is available on the PM study rescouces of ACCA website.
Hope that helps