I’m a speech-language pathologist, and his disfluency could be environmental and resolve itself once things go back to “normal,” or it could be developmental (his age and gender are most common in developmental disfluency) but if you’re able it would be worth looking into speech therapy via teletherapy for now and in a clinic/school setting later if needed. The other suggestion I have is to try to speak very slowly when you talk with him, so slowly that it almost feels awkward. Your son may begin to mimic your slow, relaxed speech without even realizing it.