If you need to accompany a passenger to their gate but aren’t traveling that day, airlines have differing rules in place for issuing passes to get past security checkpoints.
If you run into trouble, though, just buy a fully refundable ticket then check in and go through security… and refund the ticket. You can do this to go airside any time you want.
It’s never been clear to me how prohiting non-traveling passengers airside helps with security, terrorists can certainly buy tickets. I’ve always assumed it was to reduce TSA workload by reducing the number of people going through checkpoints. It’s an instance where customers are inconvenienced rather than addressing poor TSA procedures and staffing issues.