MacBook M4 Pro Dual Monitors Not Working

two more items that complicate your experiments:

The Mac does not rely on Windows-like side-loaded "Drivers" which are actually packages of resolutions and settings for a specific display. Instead, it goes straight to the immutable source -- it asks the display itself.

To get a Mac display to become active, you need the Mac to query the display, and the display to answer with its name and capabilities. Otherwise, the display will not be shown as present, and no data will be sent to the display. "No signal detected" is generated by the DISPLAY, not by the Mac.

This query is only sent at certain times:

• at startup

• at wake from sleep — so momentarily sleeping and waking your Mac may work

• at insertion of the Mac-end of the display-cable, provided everything on that cable is ready-to-go

• hold the Option key while you click on the (Detect Display) button that will appear in Displays preferences (from another display)

the second:

When a modern Mac detects a transmit error, it reacts by either dropping the data rate, or disconnecting the display.

DisplayPort cables are strictly length limited to assure that no signal attenuation will produce data errors.

ONE meter maximum for DisplayPort cables

ONE meter maximum for USB-C cables used for displays

0.5 meters maximum for ThunderBolt-3 and -4 cables, and -5 cables used as if they were the older ones.

0.5 meters max

<< Why then can't I have one display connected via thunderbolt port and one connected directly to HDMI and have them both work at the same time (completely removing the caldigit from the equation)? >>

That setup should work.

and if it does not, and your cables are already appropriately short, then you should use this desperation move:

For MacOS 12 Monetary and some later versions, some users got relief by deleting some preferences files, then Restarting:

Library/Preferences/com.apple.windowserver

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist

-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits

Restart REQUIRED after these deletions.

Can you get both to show when you reduce the resolution or turn off HDR on the Thunderbolt /USB display?

could there be any other trends that follow a particular display or cable?

if nothing there, Support was right to take your information for a Bug Report.

The data rates required to support 4K at 10 bits/color PRECLUDE using two displays over one ThunderBolt-3 cable to your Thunderbolt-3 dock. There is just not enough bandwidth for that, unless MAYBE if you drop the refresh rate very low, like 24 Hz.

if you are NOT editing magazine-cover Art daily, YOU MIGHT be able to drop back to Miliions of colors HDR=OFF.

perhaps that is what worked on your M1 PRO.

A thunderbolt cable used to connect USB-C inputs effectively becomes a USB-C cable -- it does not take on any additional capabilities if the display's input is a USB-C.

It turns out DisplayPort 1.4 includes mandatory Display Stream Compression, so of course it is not called out separately. Sorry for that oversight.

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I don't like to get in the habit of deleting plist files as a real solution, but some users got relief by deleting two preferences files, then Restarting:

Library/Preferences/com.apple.windowserver

~/Library/Preferences/com.apple.windowserver.<UUID>.plist   -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist   

-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits

Restart REQUIRED after these deletions.

if you need help finding those plists, just ask !

That M4 PRO should support HDMI 2.1 directly from its HDMI port. that would mean that 4K with HDR=ON should be attainable, and up to 120 Hz is easily attainable, and up to 144 Hz if the display can handle it, without requiring compression.

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HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

<< I would think that if I could get two external displays with up to 6k at 60hz over thunderbolt, I would be able to get two external displays with 4k at 60hz over thunderbolt. Am I wrong in assuming that? >>

when you get two displays at 6K at 60Hz, that's over two ThunderBolt cables, not one.

You CAN get two displays 4K at 60... but it also requires two cables for higher than about 60 Hz.

The other complicating factor is that HDMI and DisplayPort (including DisplayPort over Thunderbolt do not run at continuously variable speeds. There are fixed speed brackets, and your desired resolution and refresh have to fit COMPLETELY inside one of the existing brackets.

<< How do I reduce the resolution? >>

When you use Scaling, the Mac draws into a different sized window off-screen, the re-scales everything before it is sent to the Display Buffer. This can make text look much larger with smooth edges, or smaller.

When using 'scaled', the 'natural' resolution of the display itself is NOT changed.

You want to look for the slide-switch for 'Show all resolutions', turn that on, and make adjustments there.

The official story:

Change your Mac display’s resolution - Apple Support

that MSI MAG 274UPF E2 appears to be a 4K display capable of up to 160Hz under certain conditions, that can use Biillions of colors 10/bits/color with HDR=ON

Interfaces include:

1x DisplayPort (1.4a)

2x HDMI™ (2.1)

1x Type-C (DP alt.) w/ PD 15W charging

First, we need you to verify EXACTLY what model-year MacBook Pro model you have, and what processor {plain, PRO, MAX, ULTRA}

A connection to the display using a USB-C cable (or equivalent) can produce 4K at 8 bits/color at refresh rate of 75Hz. (or 10 bits color can reach 60 Hz), Higher refresh rates require Data Stream Compression, which I did not see in the specs for your displays.

Those may have changed under certain conditions, such as multiple displays.

I would say try deleting the appropriate-looking ones you find and Restart to have it create a new one, in the hopes that it's a better one.