The “auto”, “preview” and “edit” modes are not enough. I would like a mode that has no edit mode at all, never enters it and never shows the icon which toggles the edit mode. No edit mode! Why you ask? Because like in core Gutenberg blocks, the html attribute
contenteditable="true" is used to natively make text elements editable. This is IMO the most elegant solution to editing text content and thus removes the need for an edit mode and even meta boxes.
You can use false as a mode value.
There does not seem to be any difference in behavior between “auto” and false values.