Did he see a cardiologist about the chest pain and shortness of breath? That could have been a heart attack. If he didn’t it’s still worth having it checked out now even if it was years ago.
The sleeping issue could be sleep apnea or another sleep disorder. If a sleep specialist rules that out then it could well be Long Covid. LC is diagnosed through a process of elimination — if all your tests are fine but you’re still sick then it’s LC.