Same problem here. I test drove the car in the winter, no sun. Now it is really very distracting. And agree it is dangerous.
The effect can be reduced by adjusting the seating height. Improves, but still terrible and for me not a comfortable solution.
The effect is called veiling glare. I first noticed this effect back in the early 00's with a Volvo V70 that had a raked windscreen and a light coloured dash board.
You can find some info here.
Ford took a big interest in the late 1990s.
The veiling glare effect in automotive vehicles consists of diffuse and specular scattering of sunlight onto and from the windshield. This effect occurs over a wide range of solar elevation angles and increases with increased degree of inclination of the windshield. Thus its effect on visual acuity
www.sae.org
And they developed a veiling glare index along with some patents on ways to reduce the effect.
A vehicle glare reduction system is provided, which improves the visual acuity of the vehicle operator in vehicles having a light-colored dashboard. The system includes a dashboard having an upper surface from which dashboard light is reflected; a windshield having an inner and outer surface...
patents.google.com
The problem with the EQC as far as I can see is a shiny grey dash. With a perforated surface that accentuates the effect. The windshield installation angle and the driver position must be having an effect also.
Solutions to me seem to be.
Fit a windshield with an antirefective coating with the optics tuned to the angular set up of WS vs dash. Quite possible. It will significantly reduce but not totally eliminate the effect.
Cover the offending dash board with a matt black cloth. An old T shirt or a bit of black carpet. Not a very attractive addition to an expensive car.
Spray paint the dash with a matt black paint. I think a BBQ paint would good, but no idea if will stick to the dash.
Complain to Mercedes and get them to make a matt black dashboard with no silly holes or go and research the Ford idea of fitting polarising filters to the dash
I'm "happy" that other otherwise delighted EQC owners have the same issue.
Hope this is of some use and I hope someone from Mercedes reads these forums. You made a mistake that is spoiling an otherwise super car
Mikey