What do I need to have to get 3 external monitors to work in extended mode?

TheRealCodeMonk wrote:

I also saw that the M4 Pro says it can only do 2 external displays, but that's at large resolutions I do not use. I really do not need the M4 Max as it's overkill for what I do. My Mac Mini is an M2 pro and it works just fine for everything I have done with it.

All available evidence suggests that the M2 Pro, M3 Pro, and M4 Pro chips can drive a maximum of three displays total – including any built-in one.

The M2 Pro Mac mini has no built-in display, so all three of the chip's video outputs are available for external ones. On 14" or 16" MacBook Pros, one of the video outputs is dedicated full-time to the internal display (whether the lid is open or closed), leaving two video outputs to support external displays.

If you need three hardware-supported video outputs on an Apple Silicon Mac notebook, you need a Max chip. You may not want everything on the Max chip – but with the System on Chip design, things are going to be bundled to a certain extent. I do not believe that it would be feasible for the semiconductor manufacturing plant to custom-build SoC variants with every possible combination of CPU cores, GPU cores, I/O controllers, and display controllers. The economics of design, testing, and production strongly favor mass production of a more limited set of designs.

For better, or for worse, Apple decides what the designs are – and they put the largest number of display controllers into the SoCs with the highest SoC-RAM bandwidth and the largest number of GPU cores.

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Have you considered another possibility – consolidating your display space onto two larger monitors? If there were only two monitors, you would not need a Max chip – and you might be able to plug both into a Thunderbolt dock so there would be only one cable to plug into the MacBook.

If you are using three 24" 1920x1080 displays now, you could replace them with two 27" ones. Two 2.5K displays, or two 4K ones operating in Retina "looks like 2560x1440" mode, would have 18.5% more "workspace" than three 24" 1920x1080 ones. If you ran two 4K monitors in Retina "looks like 3008x1692" mode, you would have 63.6% more "workspace" than three 24" 1080p monitors give you.

There is one other thing you might want to know. I believe that you can have one AirPlay display or Sidecar display in addition to the hardware-supported ones. (Sidecar is a feature that allows you to use an iPad as a display and an input device for a Mac.)

These are software-based methods, and they aren't as good as a hardware connection to a monitor. The quality of an AirPlay display might, or might not, be acceptable. But you did say that your third monitor is a 21" one – which I take to imply a resolution of 1920x1080 pixels – and that it is a "teams/outlook/other monitor" that you do not look at very often.

Given all of this, you might be able to drive that 21" monitor by adding something along the lines of this cheap ($20) low-end Roku streaming stick. This thing doesn't support 4K, but I doubt that your display is a 4K one - and $20 is a lot less to risk on something that might not pan out than $129 to $149 for an Apple TV 4K set-top box.

Roku – Roku Express

You could test this with your current Mac mini – and if you found it workable, you could then make a decision to go for a MBP that can "only" drive two displays with the lid open. You'd connect your two 27" displays in a first-class manner through a Thunderbolt dock, and your 21" display in a second-class way via AirPlay.

Getting a Max chip would be safer in the sense that if you ever wanted to replace the 21" display with a bigger one, or if you wanted the best possible video quality on the third screen, the Max chip could support that. But if you did go the AirPlay route, you wouldn't need to run a special driver (as you do with DisplayLink and the like). The driver for AirPlay is already built in.

The only Apple Silicon MacBook notebooks that support three external displays are 14" and 16" models that have M1 Max, M2 Max, M3 Max or M4 Max chips. (The M4 Max ones are current; the others are discontinued.)

Manuals, Specs, and Downloads - Apple Support

To date, the rule regarding connecting multiple monitors to one Mac host port is as follows. You can connect two displays to one Mac host port if all of the following conditions hold:

• That port is a Thunderbolt port,
• The device immediately attached to it is a Thunderbolt device, like a hub or a dock,
• The Mac supports two or more USB-C or Thunderbolt displays, and
• The displays have resolutions of 4K @ 60 Hz or less

Since you plan on using three external displays, plan on plugging at least one of them directly into the computer.

14" and 16" MacBook Pros with the M4 Max chip have Thunderbolt 5 ports, and given that Thunderbolt 5 has much more bandwidth than Thunderbolt 3 and 4, it might be possible to connect three or four displays to a Thunderbolt 5 dock that was plugged into a M4 Max MacBook Pro. In the absence of more detailed Support documentation, or of people reporting real-world results, it is too early to say.

DisplayLink technology creates a "fake" display buffer in RAM, sends the data out over a slower interface to a stunt box with DisplayLink custom chips that put that data back onto a "legacy" interface. It is not a true "accelerated" display, and it can suffer from lagging. Just adding the DisplayLink Driver is not adequate to get a picture -- you need a DisplayLink "stunt-box" or a Dock that includes DisplayLink chips.

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It may be acceptable for a second display showing slow-to-change data such as computer program listings, stock quotes, or spreadsheets, but NOT for full motion Video, not for Video editing, and absolutely not for gaming. Mouse-tracking on that display can lag, and can make you feel queasy.

In a pinch, it may even play Internet videos (as one user put it) “without too many dropped frames".

If you are only doing program listings spreadsheets, stock quotes, and other slow to change data, DisplayLink can work for you, but requires you to make some strong compromises.

Servant of Cats is doing a great job, and I think you pretty much 'got it'.

It's very important that you understand that the number of displays supported strongly follows the Processor TYPE: {plain, PRO, MAX}