I like dual monitors. As someone who pays for electricity, I also like the new1 Apple silicon’s power efficiency. Now, having dual (or more!) monitors isn’t exactly a revolutionary thing - especially in a home setup - so colour me surprised and/or disappointed when I tried plugging in a second screen to my new MacBook Air and being met with a blank screen.

Context

Before I was indoctrinated into the Apple ecosystem I used a cheapo used Dell USB-C docking station2 I got off eBay with a Ryzen-based HP laptop running Fedora Linux. This worked a treat, and I was happily using dual monitors off the single USB-C cable. My two displays, keyboard, mouse, 3.5mm audio, gigabit networking and enough juice to keep the laptop charged all at once. Life was a dream.

Then I got a M2 MacBook Air, and tried using the exact same setup that worked with a laptop a third of the price. This is where the fun begins.

The Reason It Doesn’t Work

According to Apple, the M2 (and by extension M1) only support a single external display out along with it’s own laptop screen. This might sound like a software limitation, but it’s actually since the M1/M2 GPU is wired up in such a way that it only supports a single display alongside it’s own. It seems the M3 MacBook Air has had it’s wiring redone to allow muxing a second external display through the internal display’s chip - hence why the M3 only supports two external displays in clamshell mode.

By the way, this doesn’t apply to the Mac Mini. They can do two external displays natively - one through HDMI and one through Thunderbolt (DisplayPort).

Mitigating the Limitation

There are actually two ways around this limitation - and you might already have the means for the first one!

AirPlay Display

If you already own an iPad or Apple TV, you can use AirPlay to stream a virtual extended second screen to your device over WiFi. This works, and it might even be satisfactory for your needs, but I don’t own either device - so YMMV. One solution would be to hook up an Apple TV with HDMI to your second monitor and stream to it - definitely overengineered though.

What if I told you there exists a technology that allows a display to be connected over USB-A?

  • Yes, it is cursed.
  • Yes, it is hacky.
  • Yes, it works.

From my understanding, basically DisplayLink is a display adapter that connects over regular old USB and acts as a display. Keyword acts, DisplayLink requires special drivers installed to get any display out. Oh, and these drivers cause macOS to constantly report the screen as being recorded (it’s not wrong). So if you’re security-conscious like me, steer clear. Otherwise, install the drivers and enjoy multiple displays out. DisplayLink is available with a dongle or integrated with a few docks - I had success with a Dell D60003 for about 30 minutes before I got sick of the screen recording notification.

Enter the M1 Pro

So, I didn’t own an iPad (nor did I want to spend the exorbitant price for one) and DisplayLink worked but was prohibitively annoying. Naturally, I bought a M1 Pro MacBook Pro4 also off eBay.

Quick note: there’s the M1 MacBook Pro and the M1 Pro MacBook Pro. The M1 Pro is a different chip than the base M1, I sorted the difference by the colour of the keyboard well - a black well indicates a M1 Pro (or Max) chip. Very confusing (and is essential to differentiate for multiple displays).

The M1 Pro natively supports up to two external displays along with the internal screen. Should work now, right?

Wrong.

There’s More?

I use a dock so I have a single cable for peripherals, displays and power. Part of the secret sauce is DisplayPort Multi-Stream Transport (MST), where multiple display signals can go over a single cable. MacOS does not support MST (because of course it doesn’t). I don’t want to plug in more than a single cable into my Mac. It seems we’re at a standstill.

Thunderbolt to the Rescue

Thunderbolt is a proprietary Intel-developed interface that can allow for higher-bandwidth transfer speeds than traditional USB3. DisplayPort over USB-C is known as DP Alt Mode, and does not require Thunderbolt to work.

As it turns out, Thunderbolt docks have a special upstream port that lets you connect peripherals that show as being directly connected to the device itself (most of the time). This means I can have the single Thunderbolt dock with a regular DisplayPort monitor connected like usual, then a USB-C to DisplayPort cable to connect my second monitor to the Thunderbolt Upstream port. Typically you’d save this port for something special, like a high-speed NIC or a NVMe external SSD enclosure to take advantage of the up to 40Gb/s bandwidth available to it. Instead I’m connecting a 4:3 monitor from 2005.

For reference, I’m currently using a Dell WD19TB5 with zero issues.

Addendum: 24 Oct 2025

Since I first wrote this post I have upgraded my everyday laptop to a MacBook Air M4 hooked up to a single ultrawide monitor (still through the same WD19TB dock). As far as I know this post is still valid for getting multiple display signals out of a single cable solution, but now the M4 supports 2 displays as well as it’s own integrated display.

  1. Almost 4 years old at time of writing. ↩︎

  2. A Dell WD15/K17A to be exact. ↩︎

  3. Again, not a Dell shill. ↩︎

  4. Yes, I did technically downgrade. No, I don’t notice a difference. ↩︎

  5. I swear I’m not a Dell shill, their docks are just the cheapest on eBay. ↩︎