Under "ordinary" circumstances, the child is treated as living with you if they are away for a "temporary absence." Normally that means staying with grandma or going to summer camp but it also includes boarding school and college. I'm not sure why it would not apply here, so long as the child meets the age test (is 18 or less on 12/31/2020) and does not support themself more than 50% with an income, and is not staying with a "close" relative who could also claim them as a dependent (In this case, a "close" relative is the child's grandparents, aunts or uncles, or older sibling.)
