Could be rust on the brakes since they don't get used much (regenerative braking doing it instead). I tend to hear it after the car has gotten wet and been sitting for a while as well.
We have 2 CMaxs (2016 & a 2017, both bought used in 2018 and 2020) and they both make a scrapping sound when moving slowly with the windows open. I tend to view anything both cars do as 'normal' and don't worry about it.