I should mention that the Jimny is unwell.
It sounds like it's choked up and I was getting multiple fault codes for emissions and exhaust recirculation system too. It wasn't running at all well and would stall itself.
It's been unwell for a few months but it's only now I've managed to get a start on things.
I pulled out the O2 sensor on the combined manifold/cat, this is prior to the first cat. The second is in the exhaust system and that's what I suspect is choked up and collapsed.
The first stage has collapsed before with others, then it goes downstream into the second stage, but this looks okay to me being honest. Can't get a better view with my borescope but it seems fine,
Which is a good thing as they're £400 pounds new. The second stage cat is cheaper with a knock off part being £100ish.
Next step is to split the system and see what's going on with the second stage cat.