The editor is grey. Why do you want to press stop playing? The animation can be edited only after the play is stopped. To edit the animation. It is necessary to stop playing first.This is not very humane.Thanks for your help.
I am sorry, but this is done by design.
Groups and Tracks specifically can not be modified while the cutscene is in preview mode, but everything else is possible to edit even in preview mode. Adding, moving, deleting animation clips, editing keyframes, editing clips etc are all possible in preview mode for example.
Thanks.