Another pop-up menu appears with the monitors you can select. You can choose one of these and the app icon in the Dock will change to a monitor that graphically shows the load that component is under.

When you change to an external monitor, Desktop icons may move. Here's what you can lock desktop icons in a Multiple Monitor setup on Windows 11/10.

On the menu, you'll see an item for Dock Icon. Select it and several choices appear (see image at the top of this post) -- Show CPU Usage, Show CPU History, Show Network Usage, and Show Disk Activity.

Control-click (or right-click) on the Activity Monitor icon in the Dock and select the Dock Icon option from the menu. (Alternatively, choose View -> Dock Icon from the app’s menu bar.) ...