I made that decision based on the multiple YouTube videos. My initial test was done in parking with 2000 rpm. This is how those geniuses tested their CATs.
But today I decided to make a 50-mile highway trip with the continuous Torque real time monitoring.
This is what I got today:
and
It looks fine to me.
This is how understand it. Correct me if I am wrong.
When a car under the normal load with the hot enough cat, with the right AFR, a cat works as it is supposed to work - no O2 in the outlet, it was used by the catalytic to do its job.
When a car in park with the minimum load on the engine and the cat temp is low, it has nothing to burn in the cat, excessive O2 is coming out of the cat outlet (it doesn't matter how the engine is hot).
I made 100 miles after clearing P0420 and no code so far.
I realize that this cat is quite old. Considering that lately I used this car only for the city driving with frequent start/stops, I think that the ECM detected some abnormality.
I always used top-tier fuel and it doesn't burn oil. Will continue to drive it on highways occasionally to make the ECM happy.