Is an HDMI dummy plug necessary to run Mac Mini headless? : r/macmini
HDMI Dummy Plug 4K High Resolution Virtual Monitor Display Emulator New Generation Headless Display Adapter Compatible with Windows Mac OSX Linux, 3Pack - Walmart.com
Pi+® (PiPlus®) 4K HDMI Dummy Plug
Amazon.com: XEYOU HDMI Dummy Plug Display Emulator for Headless PC 4096x2160@60Hz, 3 Pack 4K Virtual Screen : Electronics