2020 Vauxhall Corsa frequent "engine fault" warning (but no actual fault) -

Should have asked them why it was only the one side needing replacing and what caused it . If a defect , possibly a warranty claim

Was diagnosed on 1st mot at 3 years, so probably out of warranty but my thought is it shouldn't have worn (corroded disk) at such low mileage ; still getting 'engine fault' warnings (winter again!) and was hoping to identify a systemic problem via other owners.

I seem to be having same issue. My vehicle is 2020 plate corsa and just gone in for its MOT, failed due to rear break pads and disk badly worn. Seems odd that this has happened, I believe likely a defect but out of warranty. Now there is a warning light cant get rid of which doesnt appear to have code.

Seems odd that this has happened, Why , they do wear . What is the warning light ?

I believe that either substandard or thinner metal disks used ; overall lightness of build improves fuel figures, and cheaper components help lower production costs.
After investigation it seems this problem is quite prevalent with current model corsas (Peugeot built in Spain)but not with the previous model.

Thinner discs , sub standard discs and pads would / should be subject to a safety recall if fitted . The weight difference would be negligible and not affect fuel figures ,Check with your dealership if you think this is a defect and a known fault , Brakes are classed as a routine service , wear and tear item by all major dealerships and not covered by warranty unless possibly a defective part .

By 'sunstandard' I mean thinner disks or less quality metal that seems not to withstand the rigours of British weather - it doesn't necessarily make them 'unsafe' (and subject to recall) until they actually degrade - which seems to be far too quickly !
They seem to rust / flake on the inside, and naturally the rough surface will automatically cause pads to wear more quickly.
Although, as you say, their individual weight may not be significant, it could be part of a general, larger, exercise in weight reduction and cost saving. (I had two Mazda 323 cars - a Y reg followed by a 53 plate, and it was very obvious that thinner metal body panels had been used for the newer car.)

Hope you enjoy your Corsa .