transmission fluid in my 2019 Hyundai Elantra. it has 66,000 miles.

There is always suggested service intervals on fluids, I however don't agree with them, automatic transmission fluid is on that needs to go on a "type of driving" recommendation, if you drive it mostly in town it needs serviced sooner like 30000 miles, combo driving 45000 and all highway at 60000. So if it has never been serviced do it now, and make sure it is a full service, where they remove the pan and change the filter and fluid, not just drain and refill service.