This documentation will introduce the usage of HDMI Input.
HDMI input preview can only work under framebuffer console, so you need to use the server image, you can install via OOWOW.
If you use the desktop image, you need to switch to the framebuffer console.
sudo chvt 3 echo 1 | sudo tee /sys/class/graphics/fb0/blank echo 0 | sudo tee /sys/class/graphics/fb0/blank
If you want to go back to the desktop sudo chvt 2
sudo apt update sudo apt install hdmiin-demo
sudo hdmiin-demo
If everything is OK you will see the HDMI Input source on your display.