Here is the advice from a college admissions professional. Read the final paragraph in the original post: http://talk.collegeconfidential.com/college-essays/2161062-supplemental-essay-tips-plus-the-covid-question-on-the-ca.html#latest
I think you have to leave it to your son to decide.
ETA: Do good grades needs to be explained during a crisis? The fact that he maintained good grades speaks for itself. I don’t have an answer, just adding another perspective.