After some testing I can.conclude:
1: It is a auto dimming mirror.
2: It is actually working!
Whoho!
Im blaming my inability to realize this on our long light Nordic summer nights.
Which leads to question no 2?
What is the missing dome for? Is it supposed to have something inside? A lamp bulb??
Nevermind, found out.
https://z4-forum.com/forum/viewtopic.php?t=112639