Are you asking about your own tax return or your son's tax return? You keep switching between "I" and "he." Whose name and Social Security number are on the Form 1099-DIV?
Which box of the Form 1099-DIV is the $550 in?
In general if your son had $550 of income from an investment, That income is taxable. It doesn't matter whether he takes the money out in cash, reinvests it, or does something else with it.
If you are talking about your son, why is he even filing a tax return? If his only income for the year is $250 from working, plus $550 from an investment, he is not required to file.
Can you or anyone else claim your son as a dependent for 2021?