Do you mean that if you change it to something else in the Button Function area, it does not do that different function either? If so, it sure looks as though the button is broken (I mean, it doesn't seem that the video mode is broken). But if you switch it to something else and that works, then it seems that the button is functioning but the video is broken.
As a test, if you assign video to some other button (if possible; I'm not sure it is possible), does the video then work with that button? If not, then the video is broken.
Can you do it temporarily to see if it works? You're going to have to do this by the process of elimination.The red button can be assigned like every other button - but not video.
I can assign F2 for video - but of course I don't want that.
Yes, as @Brownie says, TRY it!! If it works, then you'll know that the red button is broken and the video function is OK. If F2 does not work for video, you'll know that the video function itself is broken.I can assign F2 for video - but of course I don't want that.