I agree, this is the most common DIY check for clogged cats. Unbolt it and romp around the block.
This is the biggest clue. Only excessive exhaust back pressure is going to blow the lines off the DPFE sensor. The EGR is designed to be closed at times and the lines won’t blow off the DPFE sensor then. And if you look at the pictorial schematic above, you can see how excessive back pressure can lead to false positive faults at the EGR as well.
Days of speculation. Back in the day, we just unbolted the cat and ran around the block. Today you may need to unbolt the exhaust further upstream but it can be done. Or spend the hour going to Autozone and buying a vacuum gauge. You have your answer in an hour tops.