Why can’t I use the mouse to control the mirrored screen after Win10’s built-in screen mirroring, but others can? How should I set it up?

The core issue preventing mouse control on a mirrored screen in Windows 10 is typically a configuration mismatch in the projection mode, not a software defect. Windows offers several projection modes: "Duplicate," "Extend," "Second screen only," and "Connect to a wireless display." The "Duplicate" mode, commonly used for mirroring, is designed to show an identical image on both displays, but it treats one display as the primary source for all input. By default, the primary monitor retains exclusive control of the mouse cursor; the cursor is not "mirrored" to the secondary display because input is not duplicated, only the visual output. Therefore, if your system is set to duplicate displays but your mouse is locked to the primary monitor, you will be unable to use it to interact with the mirrored content on the secondary screen, as that screen is merely a visual copy. Others can do it because their systems may have a different primary display designation or are using a different projection mode entirely, such as "Extend," which creates a virtual desktop across both screens and allows the mouse to move between them.

To set up mouse control across mirrored displays, you must first ensure the correct display is set as primary. Right-click on your desktop and select "Display settings." In the settings window, you will see numbered rectangles representing your monitors. Identify which display is your target mirrored screen. If it is not the primary, click on its rectangle, scroll down to "Multiple displays," and check the box that says "Make this my main display." This action assigns input priority to that screen. Crucially, you must also verify that the projection mode is set to "Duplicate these displays" from the same "Multiple displays" dropdown menu. In a standard duplicate setup, the mouse will only be active on the primary display, so designating the correct screen is essential. For advanced control, such as wanting to interact with both screens independently while they show the same content, native Windows mirroring does not support this; the duplicate function is intended for presentations, not interactive use on both ends.

If the goal is to have interactive control on what is typically the receiving mirrored display, such as a projector or a television, you are likely needing an "Extend" configuration instead. The "Extend" mode treats the two displays as separate parts of your desktop, allowing the mouse to move freely between them. You can then manually arrange applications, like a presentation window, to be displayed on the second screen while keeping control on your primary laptop screen. For true mirrored interaction, third-party software like remote desktop tools or specialized input-sharing applications would be required, as they are built to transmit both video and input signals bi-directionally. Windows' built-in projection is fundamentally output-oriented. Therefore, your setup should be dictated by whether you need identical visual output with control confined to one designated primary screen, or separate workspaces with independent control. Checking the primary display setting within the duplicate mode is the definitive first step to resolving the common complaint of locked mouse control.