Yes this would be a highly desirable feature (per-activity, not site-wide)
A lot users have "pre-tests", for example, and they want students to be kind of graded there, but they do not want to include that grade into the gradebook. You probably saw such requests in this forum a lot
Other people use forums grades for simple feedback and do not want those to be transferred as well.
Other LMSs have similar per-activity flags for graded activities.
Thank you so much for looking into this!