How much information to give a mechanic

Hi everyone..

First time needing a mechanic so I'm not sure how much information to give the mechanic.

I've got the the check engine light on. P0420.

When I look at the freeze frame data, the short fuel trim is -5.5 while the long fuel trim is +28, MAP was 0 and BARO was 99Kpa. Black exhaust pipe with light petrol smell. Goggling and and using GPT suggests its the engine running lean.

I haven't been able to view live data as the scanner failed to connect to the car when I tried again.

I don't want to dig into looking for vacuum leaks or fuel pressure myself and would rather leave it to a professional.

My question is, should I say all this or just tell them there's a p0420 on the dash and see what they come up with?

Part of me thinks a decent mechanic should be able to pull those info quickly

While another part feel it could make it easier to solve the issue if I just let them know everything that could be wrong.