If you think putting your car key through the washing machine is bad...

[decrep]

Good idea Ian

 

[DixieTGS]

It's odd that they wouldn't have removed the button entirely, if they disabled it.

For Android, the method to get to the Digital key pages is different depending on the theme in use:
For the white theme, tap on the words Digital key above the words keyless start.
For the 100 years theme, tap on the octagon containing a key fob and Bluetooth symbol.

You should then be on a page where you can choose the car to manage (there could be more than one if a friend has enabled you to use their MG).

Selecting your car should take you to a page where you can activate/disable your Bluetooth key, then connect/disconnect the car's Bluetooth.

The lock & unlock buttons on this page always use Bluetooth, whereas the buttons on the main page will use the eSim if Bluetooth is not connected.

If you bother to try again and have more problems when you come to use it, I'll go to the car and refresh my memory on any lurking gotchas you may encounter.
I

 

[Everest]

If it was the circuit board in my opinion it would either work or it wouldn't. (I'm sure @Everest will correct me )

That would certainly be my stance - especially for a relatively simple circuit. You can get component failures that are temperature dependent - so only present a problem when they get hot, but unlikely IMHO to be the case here. Fingers crossed.