Tinted/Black panes in front

No question: I saw an Audi last time (sometimes new) I think I saw an A6 with which you could hardly see inside, because the front windows were completely darkened.The front window was also dark but not like the sideways in front, so drivers and co-drivers. Now my question: I was always of the opinion that this was not allowed at all. Or am I lying there next to my guess?Then I could do that with my omi too or????