I would say the first thing to check is the EGR system (assuming the car is supposed to be equipped with one). This is because usually it is easy to test.
With the engine at idle, manually actuate or apply vacuum as needed to get the valve to open. If the engine stalls aor at least runs rough, it's likely the EGR system is not plugged. Also confirm the valve diaphragm is working properly.

I would say that it is a common failure point (especially on older cars) due to the environment it has to work in. I have seen the EGR passages completely clogged on my old Camaro, the valve still worked but nothing could flow.

Now some cars I know either weren't designed to need an EGR valve or don't need it much, fine.

However, it's easy to check and a nasty environment so I would still check it first if I had NOx issues. Swapping out a cat or O2 is way more difficult and costly.

For the cars that have electronic EGR, well then I guess it's tougher to manually operate the valve. Sucks to be you. Maybe there is a jumper you can use.