Thunderbolt Display on M4 Mac mini

If this is an Apple Thunderbolt Display (27-inch), model A1407, you purchased the wrong kind of adapter.

That monitor requires Thunderbolt input. A USB-C (male) to Mini DisplayPort (female) adapter will have connectors that physically fit, but it will present a plain DisplayPort signal to the monitor. That's not what the monitor wants, so you won't get a signal. What you need is an Apple Thunderbolt 3 (USB-C) to Thunderbolt 2 Adapter .

You may want to confirm that this is a Thunderbolt Display by

• Counting the number of heads on the hydra cable. There should be two – the video one which you need to hook up, and the MagSafe one which you won't be using. If there is a third USB head, that would be an indication that you had a LED Cinema Display.
• Checking for FireWire 800 and Gigabit Ethernet ports. The Thunderbolt Display has both, while the LED Cinema Display has neither.

If this is a LED Cinema Display and it is not working with a USB-C to Mini DisplayPort adapter, then there might be a hardware issue (e.g., with the monitor) going on.

Please give AppleCare a phone call. AppleCare Contact Info