USB-C Digital AV Multiport Adapter not connecting to monitor or battery

Hi JuliaL_84,

Thanks for posting in Apple Support Communities. Since you are using an adapter, we'd also recommend checking the specifications of the adapter to learn about supported resolutions as mentioned in Connect to HDMI from your Mac - Apple Support. You can then compare it to your MacBook Air's resolution.

It might also be helpful to troubleshoot the external display using the guidance in If your external display is dark or low resolution - Apple Support since the issue may be there instead. For example, this section might narrow things down.

"Detect your display

If your Mac can't detect your external display, your external display will be dark. Use one or more of these steps to try again to detect your display.

• Disconnect the display from your Mac, then reconnect it. It might help to turn off the display first.
• Put your Mac to sleep, then wake it. On Mac laptop computers, you can close the lid for a few seconds, then open the lid again.
• Choose Apple menu  > System Settings (or System Preferences), then click Displays. Press and hold the Option key to show the Detect Displays button, then click the button.
• Restart your Mac. If you can't restart your Mac, press and hold its power button for about 10 seconds to turn it off. Then press and release the power button to turn it back on."

All the best.