THE SHORT ANSWER

Apple says a USB-C or Thunderbolt adapter used for a display must support DisplayPort Alt Mode, Thunderbolt 3 or Thunderbolt 4. A hub without that, a charge-only cable or a port already used by another display gives a blank HDMI screen. Connect the monitor to the hub first and the hub to the Mac last, set the monitor to the right HDMI input, then use Detect Displays. If the monitor works on a direct adapter but not on the hub, the hub or its cable is the limit.

Manufacturer documentation · Not physically tested by NYBreaking

1. Confirm the hub can carry video from a Mac

  • Apple: if you use a USB-C or Thunderbolt adapter to connect a display, it must be compliant with DisplayPort Alt Mode, Thunderbolt 3 or Thunderbolt 4. Check the hub maker's specifications for that wording and for macOS support.
  • Some hubs use DisplayLink instead of native video. Those need the DisplayLink Manager app; see how DisplayLink works on a MacBook Air.
  • If the hub has a detachable USB-C cable, a charge-only or data-only cable will not carry video. Use the cable that came with the hub. Our USB-C cable guide explains the differences.

2. Reconnect in the right order

  1. Unplug the hub from the Mac.
  2. Connect the HDMI cable to the monitor and the hub, and connect the hub's power adapter if it has one.
  3. Plug the hub into the Mac last. Apple gives this order for its own USB-C Digital AV Multiport Adapter: plug all cables into the adapter before plugging the adapter into the Mac.
  4. Turn the monitor on and pick the HDMI input the cable is in, using the monitor's own menu.

3. Make macOS look for the display

  1. Open System Settings > Displays. Press and hold the Option key to show Detect Displays, then click it.
  2. Put the Mac to sleep and wake it. On a laptop, close the lid for a few seconds and open it again.
  3. Restart the Mac.
  4. If the lid is closed, Apple says the Mac must be connected to power and using an external keyboard and mouse for the external screen to work.

More macOS-side checks are in MacBook not detecting an external monitor.

4. Check the Mac's display limit

A Mac drives only the number of external displays its tech specs list. On a MacBook Air with M1 or M2, that is one. If another monitor is already connected on any port, the hub's HDMI screen can stay dark or mirror. Apple's display guide says to check Display Support in your Mac's specifications. Limits by chip are in MacBook Air dual monitors by chip, and the mirroring case is covered in why a MacBook mirrors two monitors through a dock.

5. Isolate the hub, the cable and the monitor

  • Apple suggests connecting the display directly to the Mac instead of through a hub or dock. If a direct USB-C-to-HDMI adapter works and the hub does not, the hub is the problem.
  • Try the hub in the Mac's other USB-C or Thunderbolt port, and try a different HDMI cable.
  • Your picture may be dark or limited to a lower resolution or refresh rate if the cable or adapter does not support the display's mode. Apple says Mac HDMI support goes up to 4K 60Hz, 4K 240Hz or 8K 60Hz only on compatible models and that you should check the adapter's specifications. A hub limited to 4K at 30Hz is common; see 4K monitor stuck at 30Hz through a dock.
  • Update macOS, and on a non-Apple monitor install the maker's latest firmware, as Apple recommends.

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Based on official documentation reviewed 2026-10-31. Steps are general; follow the manual for your exact model. No physical test by NYBreaking.

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