Does engine oil compensate below-threshold Catalytic Converter performance?

Question

I have a Toyota Yaris 1.3 VVT-i with 2SZ-FE engine. The car has 100K of mileage (I recently bought it with no service history). Most importantly, its check-engine light is on for  "catalytic converter below threshold", which has also appeared in the MOT for the past 2-3 years.
I looked for Engine oils for this car, and based on suggestions on different websites, Castrol  Magnet A5 and/or A5/B5 is the best choice. However, I've read in another post that the choice of oil (C3 vs A5, etc) should be made based on whether the car has a Catalytic converter.
My car does have a catalytic converter, but it is performing poorly, and I don't want to spend hundreds of ££ to replace it on such an old car. The question is: does picking a specific engine oil help improving the Catalytic converter performance for the MOT test?
Also, what engine oil is best for my car in its current situation?

Solar Mike · Answer

No, using a “magic” oil won’t repair the cat.
But using the incorrect oil can easily damage it.
Replacing the cat will be needed to get the car road legal.

user15393 · Answer

Catalytic converter performs best when the exhaust gas temperature is between 300-400degree celsius. Engine oil, a part from providing lubrication to the piston-cylinder also reduces the cylinder temperature thus reducing the exhaust gas temperature slightly. But the change is not very significant.
we can use specific engine oil to improve performance of engine but the catalytic convertor will not get affected much.

Does engine oil compensate below-threshold Catalytic Converter performance?

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