ComfyUI ignores traditional uses of the Ctrl+D hotkey, namely erasing text to the right of the cursor (Emacs, macOS); and favoriting bookmarks (Windows Web browsers). Pressing Ctrl+D in ComfyUI does neither of these things. Instead, ComfyUI instantly, irrecovably erases many settings and applies the default workflow.
For safety, this hotkey can be disabled:
Navigate to Settings -> Keybinding -> Comfy.LoadDefaultWorkflow -> (Trash can delete icon).