wm just manages windows, DE is usually this + a full application suite e.g. preferences UI, File Browser, web browser, photo viewer, etc, etc, etc and some kind of 'component' mechanism so that those pieces can interoperate better (e.g. file browser reads from some settings application to determine what photo app to open things with)
A DE manages user’s view of applications and, in general, the overall user experience (usually in the GUI setting); it also provides an API for applications to seamlessly fit that experience. Window management is but a small part of this.
A DE is a desktop environment and includes niceties like text editors, settings applications, music playered, and things that make an ecosystem. Gnome and KDE are the two most popular DEs. WM is a window manager and just handles well, window management. Sometimes that included decoration and styling, usually it includes moving and closing and minimizing them. Think, Mutter, Sway, or fvwm. A WM is a subset of a DE.