I have the Hybrid4 which is the same engine and hybrid as the gse. I recently did a 200 mile journey on motorways, a roads and a little town driving and got 46mpg having started with 0 miles in the battery. I do t think that's bad for a car with a combined 300bhp.
It's a timing chain not a wetbelt

Looks like yours was one of the cars that Vauxhall/ Opel decided not to fit with Sat nav. They did this on a few cars around 2022/23 because they couldn't get the parts. If you were sold the car as having day nave I would go back to where you bought it from.

Probably needs a new switch. If you bought it from a company take it back and get them to repair it

As far as I aware it's behind/ below the AC controls. Vauxhall changed mine earlier this year and removed the ac controls and the part with 12v socket. Took them about a week to get the thing programmed to the car. Long gone are the days where you took out the old head unit and put a new one in and ...

You should be able to set them up ok. If the previous owners have used it then the navigation connected service will need to be paid for if you want to use traffic updates.
Make sure the battery replacement recall has been completed if required.

The traction battery is under the back seats. The pictures in the first post don't appear to be a traction battery fire. If it were a traction battery fire the whole car would be destroyed

I dont know the exact location, sorry

Peugeot always seems to put them behind the glovebox on right hand drive cars. As the Grandland is mostly Peugeot 3008 I suspect it's in that area as well but I don't know for sure.

Have you tried new batteries is the remote (I suspect you have)?
You could try disconnecting the car battery for at least 30 minutes, that kinda does a reboot for the electronics.

The 1.2 petrol pure tech in the Grandland has a particulate filter similar to a diesel particulate filter. I assume they use the same error code on the petrol and diesel