Yes, you might be able to claim him as a qualifying relative if he meets these requirements:

• Have been a U.S. citizen or resident, or a resident of Canada or Mexico for at least part of the year
• Received less than $4,300 gross income (except nontaxable Social Security benefits) in 2020
• Received more than 50% of their support from you 
• Not be claimed as a dependent by another taxpayer
• Not file a joint return with another taxpayer

Please see What is the $500 Credit for Other Dependents (“Family Tax Credit”)? for additional information.

Would he have to have been living in the U.S. at least part of the year? He lived in Germany the entire year except for a one week visit home.

[EDITED 7 Feb 21, 2:23:00 PM, PST]  Previous response deleted.

@sethan @DanaB27