Tillamook, I'm chiming in not because I have answers but because we have a similar experience with DS17. His anxiety and socially-prescribed perfectionism make it exceedingly difficult to do anything that will be assessed at school, though he does like going to school. He avoids the chaos (eats lunch in a practice room and takes the least-populated route between classes), will sometimes avoid (ditch) a class and a teacher if he can't bring himself to turn in an assignment. In three years of high school, he has turned in 10% of written work.
He took an online course this summer, but of course one still has to be assessed. There was also an online discussion board, and he couldn't post until he was sure that everyone else had finished the course and wouldn't see his posts. He never read the teacher comments on the assignments he turned in...in the last two weeks of the course.
After many suggestions from people at school, and knowing that some of his friends see counselors, he was finally able to go to counseling last year. We told him if he didn't like it after four sessions, we would re-evaluate, probably to find a new counselor. He continued for several months, took a break over the summer, and we are considering next steps now.
After much hesitation on his dad's and my part, he now also takes medication. As his social worker puts it, "he's more DS now." The anxiety no longer makes him curl up like a prickly hedgehog; he just prickles
It was hard to get him to see a counselor. He still won't see tutors for anything, and he needs one for writing. But he's 8" taller than I am and 30lbs heavier, so I can't force him.
He also now has an IEP for the anxiety. Much of what makes him anxious is, unfortunately, part of the landscape of school. We offered one-on-one school, smaller private school, homeschool, to avoid the triggers, but he likes going to his school. He just wishes it had half as many students and no grading.
All this is to say, if you can figure out what is causing your son's anxiety, you can begin to work with the school and talk with a counselor or cognitive behavior therapist. It may be something that will still exist with distributed learning, but you may have ways to deal with it.