I’m creating a tutorial on Compose Mode, so am trying all available options in Compose Mode. When I right-click and choose “Insert Image” Compose Mode completely freezes up until I click escape key. I left it for quite awhile to see if it was just being slow bringing up the finder window, but nothing happens.
Scrivener itself has no way of inserting an image via the contextual menu, no matter the mode. Perhaps you’re using a plug-in or system level tool that adds an “Insert image” command to text editors, and it was not coded with the notion that one might do so from a presentation mode view, like Composition uses?
At any rate, the way you would do this with Scrivener’s features is to push the mouse to the top of the screen, and use one of the Insert ▸ Image from… options.