External display not detected after macOS Tahoe update via HDMI

macOS has become progressively less tolerant of video data packet loss due to sub-par cables. There have been several reports of setups that worked in Sequoia not working in Tahoe, with nothing changed but macOS. 

Best recommendation at this point is to try a new cable. Be sure to high quality cables (HDMI should be labeled Ultra or Premium, USB-C cables should be rated for high-speed data transfer), and cables should be as short as possible (≤1 m, ideally...for Thunderbolt 5, ≤0.5 m). A random cable you found in a drawer might or might not work. 

✅ Solution

What finally fixed it for me was resetting WindowServer and related display configurations:

1. Open Terminal.
2. Run these commands one by one (you will need your admin password for the sudo ones):

# Remove global WindowServer preferences
sudo rm -f /Library/Preferences/com.apple.windowserver*.plist

# Remove WindowServer cache/database
sudo rm -rf /private/var/db/WindowServer

# Remove user-specific display profiles
rm -f ~/Library/Preferences/ByHost/com.apple.windowserver.displays*.plist 2>/dev/null

# Remove ColorSync profiles linked to displays
sudo rm -rf ~/Library/ColorSync/Profiles/ByHost
sudo rm -rf /Library/ColorSync/Profiles/Displays 2>/dev/null

# Restart display services (this will log you out)
sudo killall -HUP WindowServer

<< bought different types of HDMI cable (female to male). >>

You should be using male-to-male HDMI cables of modest length. using male to female cables implies you are using additional devices with unusual connectors, which you did not name.

Best results are obtained from certified cables labelled ULTRA High Speed, and they are backward compatible for older versions of HDMI.

--------

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

Library/Preferences/com.apple.windowserver

-AND-

~/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.

TL;DR; >>disable VRR on the monitor<<

After updating my MaxBook Pro 16 M1 to macOS Tahoe (26.3.1), my external monitor (ASUS PG32UCDP) was detected by the system, but no image was displayed.

Symptoms:

• Monitor appears in System Settings → Displays
• Windows can be moved to the external display via hotkeys
• No image output on the monitor
• Sometimes works for 1–2 minutes, then the screen goes black
• Happens even at 1080p 60Hz or 30hz
• Safe Mode did not fix it
• Multiple cables tested (USB-C → DP, USB-C → HDMI, USB-C → USB-C)
• Monitor works perfectly with PC and PS5
• MacBook works with other monitors without issues

The fix:

Disabling VRR (Variable Refresh Rate) in the monitor’s OSD settings immediately resolved the issue.

After turning off VRR:

• Stable image
• No signal drops
• Works at 4K 120Hz without problems
• HDR works as well

It seems macOS has a VRR/handshake issue with certain high-refresh 4K monitors.

If your external display is detected but shows no image, try disabling VRR on the monitor itself.

Hi everyone,

Just spent 2 hours on this and found a fix that doesn't involve buying a USB-C adapter, so I figured I'd share since every thread I read ends with "just get a dongle".

My setup: MacBook Pro 14" M2 Pro, macOS Tahoe 26.5, Samsung monitor over HDMI plugged directly into the Mac's built-in HDMI port. Classic symptom, the monitor powers on but stays black, and the Mac doesn't see it at all. Nothing in System Settings, nothing in system_profiler SPDisplaysDataType, nothing in IORegistry. The same HDMI cable works fine on my TV, and the monitor used to work with this Mac before the Tahoe upgrade.

I tried everything you usually find on forums: multiple HDMI cables, rebooting with the monitor already plugged in, updating macOS (26.4.1 then 26.5), disabling VRR on the monitor, Option+Detect Displays in System Settings. Nothing changed.

What ended up working is one command in Terminal, no sudo needed:

mv ~/Library/Preferences/ByHost/com.apple.windowserver.displays.*.plist ~/Desktop/

Then plug the HDMI cable in, restart via the Apple menu, and on boot the monitor is detected right away.

Why it works. macOS keeps a cache of every display it has ever seen in this file. On my Mac there were 11 configurations stacked up across 8 different displays (old TVs, meeting room projectors, previous office monitors, you name it), and several of them were in a clearly broken state: dimensions of 1x1 pixels, origin coordinates at -3200, a mix of Sequoia and Tahoe formats in the same file. Tahoe became way stricter about validating this file, where Sequoia would just silently ignore invalid entries. So the entire display detection pipeline gets stuck on the first malformed entry it hits, and the HDMI handshake never even starts with a new monitor.

The mv sends the file to the Desktop instead of deleting it, so you have an automatic backup. If anything goes weird you can put it back:

mv ~/Desktop/com.apple.windowserver.displays.*.plist ~/Library/Preferences/ByHost/

Hope this helps someone.

Thank you for your comment! Neither of my standard USB-C cables from Apple or LG worked.

I bought a Thunderbolt 4 cable from ANKER, and it works fine now.

Totally agree. I've also upgraded to Tahoe, 26.0.1 bought different types of HDMI cable (female to male) - 4K and 8K, as well as a type c to hdmi coverter. It all didnt work in Tahoe 26.0.1 version, with the same exact setup, when boot in safe mode, Macbook Pro could pick up the external display again. Extremely frustrating trying to understand what's wrong.

nbarshain--

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)

so try doing some of those things and see if the display comes alive.

kokularaj wrote:

I recently updated my MacBook Pro 14” (M2) to macOS Tahoe. Since the update, my external display is not being detected when connected via HDMI.

However, if I connect my iPad as an external display, both the iPad and the external monitor work. Once the iPad is disconnected, the external display also stops working.

https://discussions.apple.com/content/attachment/6b595d67-aeae-493f-a303-c283f4a315e4

[Edited by Moderator]

I would verify the cable connection it has been a known issue...

the macOS is increasingly fussy over sub-par cables for external Display connection…

high quality cables certified ULTRA HDMI cables or PREMIUM ≤ 1.0 m length, USB-C cables rated for high-speed data transfer

Also for best results the shorter the cable the better, ex . for Thunderbolt5 cables , ≤ 0.5 m length

ref:

Connect one or more external displays with your Mac

you can submit your Apple Feedback here: Product Feedback - Apple

Tried this and it didn't work. I was about to downgrade to Sequoia, but I bought an ANKER Thunderbolt 4 cable, and it worked!

I have a slim little portable monitor (Lepow brand) that I plugged into my new computer with Tahoe, and it turned on but no signal detected. I then plugged it into my old computer with Sonoma (14.6.1) and it worked just fine.

Turns out what fixed it was power cycling my monitor.

I plugged it into my new computer (which turned it on straight away), then held down the power button on the monitor to turn it off, then held it down again to turn it on. It miraculously turned on and showed me my desktop!

I have an M1 Max and an M4 Pro (home and work). The M4 handled the update to 26.1 fine, but I also suffered the same external monitor issue with the M1. I use a caldigit TS4 dock, and have good cables.

I had tried everything here. Removing prefs, switching cables, messing with monitor ports/settings - I even did a fresh install of 26.1 and the problem persisted.

I just installed the 26.2 RC build and I'm happy to report it has fixed the external monitor issue, so fingers crossed they'll release it soon!

BTW, rolled back to Sequoia. Everything works like a dream again. Guess that will be my OS for next 10 years :D

Mine is an M1 Macbook. The issue was resolved after getting a Thunderbolt 4 cable.

kokularaj wrote:

Thanks for your reply. I intended to connect only one external display via HDMI, while my iPad is connected as a display over Wi-Fi. Interestingly, when I connect the iPad as a display, the HDMI-connected external monitor also works. This makes me believe it’s not a cable issue.

To be proactive you can file a bug report / submit your Apple Feedback here: Product Feedback - Apple