Less power than it should/bogging motor?

Oh wow, that buried the needle.

This thing has not set a single code during all this. I know it looks like you have the exhaust apart already, I would expect even a MAF code with back pressure that high, or even a rich exhaust code, something, With a clogged cat, if that's what we're dealing with here, the MAF would be reading low, fuel trims would be negative as well due to a lack of air coming in. I'm going to do a little more research here. This thing doesn't have a turbo does it?

This might sound silly, but there is nothing stuck into the end of the muffler is there?

It looks like the front cat is okay, because you took a reading after it and it was high, but that 2nd one doesn't look too good, If you could get a flash light behind it and see if you can see clearly through the substrate from the front of the rear cat with your camera, that would show if that rear cat is partially clogged. I can see how long the pipe is behind the rear cat, maybe if you could fish a flashlight up behind the rear cat to get a better view.

Okay, sorry. I was just going through your last few posts, so with the rear cat off the back pressure was okay?
And the live data is with everything except the front cat off?

Okay, then you have found the issue, sounds like the front cat is okay if you are taking a reading from the front 02 location and the pressure is ok with the section behind the front cat removed. I could hear the hissing sound in the video, it was loud.
If you're still unsure about making the call on that mid-section, it needs to be checked on the bench with a flashlight and you bore scope from both ends. The converter doesn't need to be completely melted down into a ball and blocking off the entire exhaust to be bad, in that case you would have a no start condition. This one could be melted down somewhat in the middle where it's difficult to see, but the front pictures didn't look good. And with that exhaust down and the back pressure gone, there has to be a restriction somewhere from the back of the front cat to the muffler. I think the front cat is the more expensive one, because it's more of a 3-way catalyst, where the rear one is just to burn off or convert whatever exhaust gases are left into water. And that's expelled out the muffler. But I think you did a good diagnosis with pulling down just the middle section and retesting, it was loud, but as long as there's nothing stuck in the muffler, that only leaves the mid-section. Through it on the bench and try to get a better view if you need to. I like to be as thorough as possible too. Especially when it comes to expensive components like this

That first picture looks like it's melted, some of the others look like the vehicle might be burning oil, contaminants like oil, coolant, a rich mixture, or misfiring cylinders will cause cats to fail, but that black dark area looks like oil. Interesting there isn't more damage to the front cat. But whatever caused this failure needs to be figured out. When you get it running right, reset the ECM so it can relearn its adaptive fuel strategy, and monitor the Fuel trims and misfire counters, even if the misfires are not bad enough to set a code, they should come up in Mode 6 data. It should be available somewhere in your scan tool, even my 20 year old first OBD2 scan tool had mode 6 data. It's designed for engineers use, but it will show misfires that are not bad enough to set codes. The Cylinder misfires are listed on the 2nd page below, they have changed somewhat, but those are the IDs you will see misfire counts on if nothing else is setting codes.
If you can, with your bore scope, look into the cylinders and see if it looks like the engine is burning oil. The top of the piston will be black with carbon build up heavy, so will the spark plugs. The fuel trims will tell you if its running rich, or if the rear 02 sensor is stuck lean (low voltage below 0.4v will send the ECM rich due to a skewed sensor). Make sure there are no leaks in the exhaust either, Cats can last if they are not overwhelmed with too much Hydrocarbons or CO.
Something else to think about, is changing the oil, after the repair, cleaning the throttle plates and MAF, with this engine not breathing properly, all this stuff is going to have gotten backed up due to the PCV not being able allow crankcase pressures to go somewhere. I'll catch up with you tomorrow if you have any more questions. But I'm glad you got this figured out, we just don't want a new cat to fail.

https://www.2carpros.com/articles/blue-smoke-from-engines-exhaust

https://www.2carpros.com/articles/engine-misfires-or-runs-rough