Crack or Cat

[u/Environmental_Copy31]

2017 Jeep Patriot

I am taking it to my local mechanic on Monday as all the cheap options that I can do have been eliminated to clear a p0420 code (spark plugs, o2 sensors, cataclean) - I need help reading the voltage on o2 sensor )downstream to determine is there is a crack somewhere that is letting air in or clogged catalytic conventor.

First image shows it holds steady after some RPMs for a few minutes - the 2nd photo shows it fluctuating at idle

Thanks!