A quick comparison: think Linux Kernel (window manager) vs Linux Distribution (desktop environment).

A window manager is part of a desktop environment.

A desktop environment is usually made up of:

- A window manager (i.e. kwin, xfwm, i3, etc.)

- A file manager (i.e. Dolphin, Nautalis, etc.)

- Other utilities, such as a network configuration tool, a print config tool, maybe a web browser, a calendar or PIM system, calculator, etc.

It's one of the components of a desktop environment, but not a desktop environment itself: https://www.ghacks.net/2008/12/09/get-to-know-linux-desktop-...