Whole Forum Grading is a relatively new Grading Interface that was introduced to us in Moodle v3.8. To enable this, follow the steps below:

1. Navigate to your course

2. Turn Editing On

3. Navigate to the Forum that you would like to change

4. Select the Edit menu inline with the Forum activity, select Edit Settings:

5. When a Forum is created, the default grading method is Ratings, you will want to turn this off. Navigate to the Ratings drop-down menu and change the Aggregate type to No Ratings:

6. Just above this drop-down menu, navigate to the Whole Forum Grading menu:

7. Once you expand this menu, select type as Point:

8. Then, choose the point value or Maximum Grade that you would like the assignment to be worth:

9. Lastly, scroll to the bottom and select a Save option: