You can connect one or more external displays depending on your Mac model. To find out how many external displays your Mac supports, check its technical specifications:
If you're using a Mac with Apple silicon, you can connect a single external display to your Mac using one of the Thunderbolt / USB 4 ports. Docks don't increase the number of displays you can connect as an extended desktop. On Mac mini (M1, 2020), you can connect a second display to the HDMI port.
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Connect your display to power, then connect your display to your Mac. Check the ports on your Mac to find out whether you need an adapter.
After you connect your display, you can choose to extend your desktop or mirror your displays.
With Apple TV, you can use your TV as a separate display for your Mac. Learn how to use AirPlay to mirror or extend your Mac display.