If the display cable provides a connector that doesn’t match the Thunderbolt / USB four ports on your MacBook Air, You need to use an adapter (marketed separately) to connect the display. Troubleshooting. To troubleshoot an issue with an external display, see Should your external display is dim or small https://keeganwtmct.goabroadblog.com/26100648/5-easy-facts-about-hdmi-to-usb-c-displayport-adapter-described