It has always depended on their age. If they were under 24 on December 31 you can claim a full time student no matter how much they made. If they turned 24 during the year you can only claim them if they made less than 4,300 in 2021.
See IRS Publication 501 starting on page 11 bottom Dependents
https://www.irs.gov/pub/irs-pdf/p501.pdf
Who can I claim as a dependent?
https://ttlc.intuit.com/community/credits-and-deductions/help/who-can-i-claim-as-my-dependent/00/267...
