Apple USB Type-C Digital AV Mutiport adapter

Is this a 24" M3 iMac?

Are there any other displays connected to this iMac? (The 24" M3 iMac has a limit of one external display.)

If you go into System Information (Option– > System Information…), and look at the display for the USB sidebar heading, do you see anything there? How about under the Graphics/Displays heading? (I don't think anything will show up under Thunderbolt/USB4 since this adapter is not that kind of device.)

Try these general troubleshooting procedures.

• try the adapter in a different port on your iMac
• try the adapter on a different iMac if you can
• restart in safe mode followed by a normal restart
• uninstall any antivirus and clean up apps
• check all cables, swapping any removable cables