I noticed that the HUD becomes much less defined when I’m wearing sunglasses to the point where it almost disappears. If I tilt my head to one side it is clearer.
I presume this is because the sunglasses are polarised.
Polarised sunglasses and HUD
Yes, most likely the glasses - I have a BMW 3 series 2021 and HUD is actually invisible with polarised sunglasses - I believe some cars can tilt the polarity to compensate.... my id.7 is due soon so I will see if they match or conflict with their polarity