Code p420 Chery tiggo 3 2022

Hello! Hello good! I need help to rule out a problem in my 2022 Chery tiggo 3. It turns out that the check engine came on 2 years ago, I have not noticed changes in speed or consumption. With several scanners it gave us code p420. It passed the gas test of my country's technical inspection, without problems. I didn't give it much importance, I even traveled from Viña del Mar to Patagonia Argentina and then Chiloe, and the car behaved excellently, he insisted that I don't see any greater expense in fuel consumption and power, it feels like always. I changed the spark plugs to discard and well... I said I'm going to buy the oxygen sensor, I changed it before a trip... on the trip after 600 km it came on again. What could it be? What tests do you recommend doing before making any other part changes? What do you suggest? Many mechanics are used to changing parts and I prefer to do tests and then move on!