If the person is "Eligible" to be claimed and is actually claimed by his parents in 2021, presuming they meet income requirements etc. they likely will qualify for the recovery rebate credit when filing out the return. If you complete the forms and questions correctly, ProSeries seems to be coming up with the correct answer.

If you want to double check the eligiblity of the person to be claimed as a dependent I have found this tool useful.

https://www.irs.gov/help/ita/whom-may-i-claim-as-a-dependent