You can confirm worn cat by charting a graph with the same bank pre and post. The pre should flip high/low/high/low many times a minute. The post cat should work towards a valve and hover near a constant value. If it tracks lockstep with precat the cat is usually shot but If it's just a little too active you can add a defouler to get a couple more years out of a tired cat.
https://a.co/d/09Qk6poG
An example. A totally worn out cat it won't help but a weak cat that still will moderate nox etc just not as well as new it will squeeze some life out of the cat.
Follow your conscience; the car will grate a little more pollution but from what I've seen not a lot because when the cat totally fails the defouler trick will not help at all.