HDMI out from laptop will not duplicate display, only extend as a second monitor

I’ve run into this issue before too usually it comes down to how Windows handles display settings. If you're using HDMI from a laptop, try going to Display Settings → under “Multiple displays” select “Duplicate these displays” instead of “Extend.” Also make sure the laptop isn't defaulting to a projector or external-only mode. Sometimes a graphics driver update helps too, especially with Intel or Nvidia cards. Hope that helps!