If your child spent 4 months at college in 2019 then graduated and lived with me the remainder of the year , can he be claimed as a dependent?

Did you provide more than half of the living "expenses" for the year?  Such as food, shelter, clothing - the basic necessities?

Graduation year is a little tricky.   How old was he at the end of 2019?  How much did he earn in 2019?