Thanks for clarifying. This one suggests the IRS has not given guidance:
https://www.journalofaccountancy.com/issues/2012/mar/20114558.html
w/ some possible bias that it’s the owner’s spending, not the beneficiary’s.
https://www.savingforcollege.com/articles/the-impact-of-529-plans-on-claiming-a-dependent also suggests no IRS guidance.