Subaru and the dreaded PO420 code

We have been driving with it, unfortunately. We were too nervous to invest the $ since we had a friend who spent thousands and still has the code. I tried talking with several different mechanics about that specific code and none of them wanted to do anything but replace the cat.

The code isn’t always there, it comes on and off. Usually clicks on if we have been driving for at least 30 minutes.

I would have to check my books and see about the plugs, I am not sure how long it has been since they and the fuel filter were changed. We have been doing all recommended maintenance.