How to separate two external monitors on a new MacBook Air 15 (May 2025) with a Dell Thunderbolt 4 dock?

If your Dell dock allows connecting more than two monitors at a time, it may be driving some outputs in a way that Macs do not suppor.

There may be only certain combinations of outputs that will feed separate signals from the Mac to each monitor - instead of taking a single signal and feeding it to both.

I believe there may be a support article somewhere on the Dell site that would give more detailed guidance for specific docks.

Go into System Settings ➜ Displays ➜ [Click on a display], then on the Use As drop down, and click on "Stop Mirroring".

click here ➜ Extend or mirror your Mac desktop across multiple displays - Apple Support

BarbVezos wrote:

Thanks. I did try that but the 2nd monitor doesn't show up when I try to detect it.

That would indicate it's the dock that's duplicating the signal and not passing the monitor to the Mac so it won't see it. The Mac needs a specific handshake from the display to enable the second output.

The second display may need to be connected in some other way to be visible to the Mac.

I would as suggested by Servant check out the specifications of the Dock.

Here's the Dell article that I was thinking about.

Dell Support – Knowledge Base – Dell Thunderbolt Docks and Apple USB-C Hosts

I found this once or twice before, and it turns out I had saved a bookmark to it, after all.

Just to check - does this MacBook Air have a M4 chip?

Ones with earlier M-series chips do not have the same video capabilities.