My (21) yr old is in the Army Reserve and deployed in Oct 2022. From Jan-Oct, he lived at home working and going to school part time, no rent or utilities. Dependent?

If he was only a part time student, he does not qualify as a qualifying child dependent. He may qualify as a qualifying relative if all of these tests are met.

1. The person can't be your qualifying child or the qualifying child of any other taxpayer.
2. The person either (a) must be related to you in one of the ways listed under Relatives who don't have to live with you, or (b) must live with you all year as a member of your household (and your relationship must not violate local law). Your son does not have to live with you for the entire year to qualify.
3. The person's gross income for the year must be less than $4,400.
4. You must provide more than half of the person's total support for the year.

In your case, it depends whether or not he made more than $4400 for the year.