[Cin] Speed line

I'm doing an intro for the YT channel and have some problems with the speed line. Is it possible that the speed line can no longer be modified in the current version? I have activated it under the menu item "View" "Speed". In the video track I see the orange line, but I can click on it as much as I want, no new keyframe will be created. Am I doing something wrong or was something changed in the meantime? Can anyone confirm this or give me some advice? Sam