MacBook Pro M4 Pro not detecting dual 4K OLED monitors

Question

MacBook Pro M4 Pro not detecting dual 4K OLED monitors

Hello,

I’m trying to run two ASUS ProArt Display OLED PA27UCDM monitors on a MacBook Pro M4 Pro (latest macOS).

According to Apple specs, the M4 Pro supports two external 4K displays over Thunderbolt/HDMI, and ASUS documentation also mentions Thunderbolt daisy-chain support for these monitors.

However, I cannot get both monitors working simultaneously correctly.

Both displays work perfectly individually, but when both are connected:

only one is detected,
or the second stays black/not recognized.

I already tested:

Thunderbolt 4
HDMI
DisplayPort
Thunderbolt daisy chain
HDR off
60Hz
different cables
factory reset

Has anyone successfully used two PA27UCDM monitors or just two 4k oled monitors with a MacBook M4 Pro?

I’m wondering if this is:

a macOS compatibility issue,
a Thunderbolt negotiation issue,
or an ASUS firmware problem.

Any help would be appreciated.

Posted on May 18, 2026 4:31 AM

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Answer 1

Top-ranking reply

Grant Bennet-Alder

Level 10

143,333 points

May 18, 2026 7:05 AM in response to MaîtreCorbeau

Thunderbolt cables for high resolution displays are limited to 0.5 meters maximum. Longer cables that contain signal re-drivers are available, and are sold as ACTIVE or PRO cables. Thet can be pricey, often starting at US$125.

There are a few cables that are less expensive.

Thunderbolt-4:

OWC.MacSales sells a 2 Meter ACTIVE cable for about US$50.

ThunderBolt-5, a better "investment' in the long run:

cable matters sells a 2 meter ACTIVE cable for about US$80

caldigit seems a 2 meter ACTIVE cable for about US$140

Apple sells a ONE meter PRO cable for about US$70

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Answer 2

May 18, 2026 6:56 AM in response to MaîtreCorbeau

ASUS PA27UCDM appears to be a 4K display at 10 bits/color HDR+ON with refresh rates 48 to 240 Hz.

Interfaces include:

HDMI 2.1

DisplayPort 1.4

ThunderBolt-4

The first 4K display on a Thunderbolt-4 cable consumes just over 50 percent of the bandwidth at 80 Hz, more at higher refresh rates. There is generally not enough bandwidth on ThunderBolt-4 to daisy-chain a second 4K display off the first display, so don't do that.

The highest bandwidth interface available at this combination of computer and display is HDMI at about 42 G bits/sec. but it requires special cables. This cable can be several meters long.

Using a Thunderbolt cable is another option, but this also requires standard ThunderBolt-certified cables 0.5 meters or shorter, which can be very limiting.

There are also reports of a bug in MacOS that sometimes commits BOTH of your two available display generators to the first very high resolution display, but this seems to affect only 5K displays.

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Answer 3

May 18, 2026 6:57 AM in response to MaîtreCorbeau

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.

Cables 'shipped in the box' with many displays can be "lowest bidder" cables that are not up to high-end display use. Cables with no markings 'found' behind your TV set are unlikely to be good enough.

HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.

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