It is SO hard! Especially with the class being virtual, he won't get any of the social/on-campus college experience!
However, he made this choice when he dropped the math class .
My teen goes to a school with an extended school year so there is a mandatory 6 week summer term. After the first year, we learned to keep the summer REALLY low key. Our family has two "must" events every summer. We do those and school; trying to have as much unscheduled summer fun as we can in between.
He will make it through the class. It will probably not be as much ZOOM time as is advertised, but don't tell him that. Encourage the positives: college experience, fewer classes in the school year, able to delve in an concentrate on only one subject!
It will work out. He will get through this. It may sound more daunting that it is.
The other thing is to remember that he is IN SCHOOL this summer. Keep your expectation "school year" expectations, try not to overschedule or overwhelm him with chores, work, ect.