System Settings no longer provides the option to add an additional display after updating to macOS Tahoe

To be very clear – the (+) you are seeing, whenever you see it, is only for AirPlay and Sidecar displays. It is NOT for displays connected by a cable. Your hub is not doing what you thought it was doing. That is true in Tahoe, it was true in Sequoia.

Here's the demonstration of that, and I did it in Sequoia to confirm for you that it was that way prior to Tahoe.

1) External display connected, AirPlay and Sidecar displays available:

2) I turned off Wi-Fi, which is how the Mac would connect to the AppleTVs. Note that only the iPad (Sidecar) remains:

3) With Wi-Fi off, I also turned off Bluetooth so the iPad is not available either. Note how the (+) button is now gone:

(Also the Arrange tab, for completeness; in your screenshot you are mirroring the displays, I am extending onto the Thunderbolt external display that is actually connected via a TB3 hub).

Likewise, the Arrange tab only shows up if there's another display connected (either wired or AirPlay/Sidecar). My prior screenshot (previous post) did not have an Arrange button because it was in clamshell mode, using only the external display. If I connect the iPad (or an AppleTV), I get the Arrange button.

It's the same in Tahoe, though the (+) button is down next to the Arrange button – the AirPlay/Sidecar choices go away when not available in Tahoe just like in Sequoia, and when they're all gone the button itself goes away as well, just like Sequoia.

So as I see it, you have two choices:

1) Troubleshoot your AirPlay connection. You may need to check the settings on your TV(s) to see why they're not showing up for AirPlay.

2) Get a (or a pair of) high quality USB-C to HDMI cable(s) and connect one (or both) TVs directly to two of the four ports on your Mac.

Personally, I'd go with option 2. If you use the hub to connect other stuff besides the one TV (as stated above, it's only driving one of them), then get one cable for the other and keep the hub. If the hub is only for the TV, ditch it and connect both directly.

TheRamblinRogue wrote:

I'm using two Samsung TV/monitors as the externals.

Since the download of Tahoe, no option for adding any additional display is available via System Settings. The + and - that would appear next to the Arrange button no longer appear.

As Luis Sequeira1 states, the option to (+) a display in the Displays preference pane allows you to add displays that are connecting via AirPlay or Sidecar. Since you're using TVs as external displays and many of them support AirPlay natively (my Samsung TVs do), I believe what is happening is that your hub/dock is being used for only one display, and AirPlay is being for the other when you Add it in settings.

Note how on a Mac running Sequoia, the external display just 'shows up' and the (+) option offers my other Mac and Apple TVs via AirPlay (the top option is the keyboard/mouse/trackpad that are available via Universal Control).

The (+) option you're looking for is still there in Tahoe, it's just been moved to the bottom of the settings pane. Still shows only AirPlay and Sidecar options (you can see my work Mac showing up, also my AppleTVs and iPad).

Incidentally, the only way to 'add' a physically connected display that is plugged in but not showing up automatically is to use the Detect Displays function. The Night Shift button at the bottom of the settings pane turns into a Detect Displays button if you hold down the Option key.

TheRamblinRogue wrote:

I also am confused by the several suggestions of "connecting directly to the Mac." How would the use of a cable or adapter differ from the use of a hub?

Macs don't support DisplayPort Multi-Stream Transport (MST). This is a feature of DisplayPort that allows you to daisy-chain two DisplayPort monitors if the computer and monitors support it.

As mentioned before, a Mac that supports multiple external monitors will only support driving

• One monitor over a plain USB-C (DisplayPort Alt Mode, or DisplayPort + USB connection), or
• Two monitors over a single Thunderbolt connection (e.g., to a Thunderbolt hub or dock), provided that each of the monitors has a resolution of 4K or less.

This is not something recent. Lack of support for MST goes way back.

Thus, if you see a plain USB-C dock that supports attaching more than one monitor at a time, that is a sure sign that the dock uses MST, a workaround, or both. If you see a Thunderbolt dock that supports attaching three or more monitors at a time, that is usually a sign that it uses MST. (It is very rare for a Thunderbolt dock to employ workarounds such as DisplayLink, presumably because customers for Thunderbolt gear are expecting high-end performance.)

Connecting one monitor to a plain USB-C hub that uses MST, and another monitor directly to the Mac, can fix the problem because then the USB-C hub is not feeding a single video signal to both monitors. Instead, the hub will feed the signal that it gets (Signal #1) to the monitor attached to it, while the computer will be feeding a different signal (Signal #2) to the monitor that is directly attached to another port.

If you have USB-C/HDMI cables, try connecting directly to the Mac. What hub, and is it using any software (e.g. DisplayLink) that may need updating?

TheRamblinRogue wrote:

I might agree with but, until I upgrade to Tahoe, that hub worked just fine and the option to have three displays, the built-in laptop plus two externals, has worked for over five years. So, while NOVOO might be a dime-a-dozen hub, that isn't the problem. Something about Tahoe is.

Backing up a step, when you connect to displays, are you seeing the same thing on both of them or different things on the two displays? Docks by the manufacturer you mentioned use MST, which means without displaylink or another software hack, you will see the same thing on any number of displays connected through the dock.

If you are expecting extended displays across different monitors, then despite what you think, the issue is your dock and not Tahoe. Or rather, it’s that the drivers your dock is using are not compatible with Tahoe, but it is not Apple‘s responsibility to ensure that compatibility.

Macs only support driving two displays from a single dock or hub if it is a Thunderbolt dock or hub, and "NOVOO" sounds like one of those brand names associated with low-end, generic, dime-a-dozen docks and hubs.

With those, when there are multiple display outputs, they either

• Use DisplayPort MST, which Macs do not support, or
• Rely on second-class "workaround" technologies like DisplayLiink

A typical symptom of connecting two displays using MST is that the Mac will see only one of them – and they will appear to "mirror" each other because the hub or dock is feeding the same video signal to both.

Sounds to me like the issue is that you added this NOVOO hub to the mix, rather than that Tahoe changed stuff. Your options would be to plug at least one of the displays directly into the Mac, so at most one goes through the NOVOO hub; or to replace the NOVOO hub with a Thunderbolt dock or hub that can drive two monitors.

I have used my MBP with two external displays in Tahoe. It works. I have used one directly via HDMI port and another with an adapter.

How many displays does it show in total in System Settings? 2 or 3? I suppose it shows 2. If I am right then it is probably not going to work using them both attached to the dock, even though it used to before

As others have said you could try connecting one display directly and another via your dock. This would certainly work.

TheRamblinRogue wrote:

As I've mentioned, my current setup of hardware hasn't changed for a few years. With the two HDMI cables attached via the hub, the only procedure I've had to use was booting up the laptop, opening System (whatevers), adding the "third" display and getting to work.

Incidentally, this definitively confirms that you were connecting to that "third" display using AirPlay. Displays that are directly connected do not need to be 'added'. If they are powered on, then they get a signal when the Mac boots up. My Thunderbolt 3 dock supports dual displays, and when I connect two displays (e.g., one via Thunderbolt and another via DisplayPort), then connect my Mac tot he dock (or boot the Mac if it's already connected) both of the displays are immediately active.

Thank you all for continuing to help me understand what might have changed.

The only thing that has changed is your AirPlay connection to one of your TVs is not working. That could be the TV, I can't see why Tahoe would affect that (AirPlay works fine for me on Tahoe).

https://www.samsung.com/ph/support/tv-audio-video/how-to-connect-mobile-device-and-tv-with-airplay/

Is this a hub that requires DisplayLink software? If that is the case, you probably just need to update DisplayLink.

Normally, you should not need to add anything, the displays ought to be recognized immediately.

As far as I can tell, there has only been an option to ADD another display if it’s using Airplay, or Sidecar. That still exists in Tahoe, and works as before.

Directly attached displays just work, they can’t be added or removed. I don’t recall ever seeing those + and (especially) - buttons that you recall.

Again, unless there is some updated driver for your dock, the option is to connect one display directly (since the Intel MBP only has USB-C ports you need a simple USB-C to HDMI adapter).

Note that an AirPlay or Sidecar connection operates by different rules.

AirPlay and Sidecar are software-based connection methods that are not as good as real hardware-accelerated video outputs, and that do not count towards your Mac's maximum number of cabled displays. I think that you can have one AirPlay or Sidecar display in addition to your real hardware displays.

With 'AirPlay and Sidecar, video does not go over a USB-C / Thunderbolt or HDMI connection from the Mac, but instead travels over your local network.

Many smart TVs have HDMI ports and AirPlay support. If you were sending "mirrored" video from a plain USB-C hub that used MST, and AirPlay for an "extended" screen, to such a TV at the same time, what you would see on the screen would depend on which input the TV chose to display.