I have a MacBook Pro (M4) connected to an external monitor via a USB-C to USB-C cable. It was working fine until I upgraded the OS to macOS 26 earlier today. However, the external monitor is no longer detected, even after I restarted the MacBook Pro.
MacBook Pro 14″, macOS 26.0
Just to help others Deep System Reset by abhiraj_chatterjee worked here too.
So the culprit was corrupted display preference files left behind by the macOS Tahoe upgrade. Not the hardware, not the cable, not the display switch. macOS had cached bad display settings and was silently rejecting the connection every time based on that stale data.
To recap the full journey for anyone who ever finds this:
Unplug monitor and run The Deep System Reset script posted by abhiraj_chatterjee:
bash
rm -f ~/Library/Preferences/ByHost/com.apple.windowserver.displays*.plist
sudo rm -f /Library/Preferences/com.apple.windowserver*.plist
sudo killall Dock
Then restart, plug back in after restart -> display works again fine.
Exactly the same external monitor problem here. Extremely disappointing!
Bought new expensive high-quality cable. No improvement.
This worked on my M4 Max MacBook Pro, thank you so much!
I confirm, this solution works. I had the same problem with my monitor Lenovo LEN S24e-10. After following this advice, the problem was completely resolved.
Thank you.
Hey everyone, I've also just experienced this issue after upgrading to macOS 26. So a few things. I am nearly certain this is not due to the cable. Everything was working as it should before the upgrade. The issue appears to occur with USB-C connected monitors, particularly when using a docking station.
Here's how I reproduce the issue. When I use my Mabook in clamshell mode, it functions as expected. Now, if I unplug the dock and then use the laptop with nothing else connected, it works. But when I replug the Dock into the computer, that's where I get issues.
A few things I've tested: unplugging and replugging the monitors - no go.
Unplugging the Dock and replugging that in, no go. Plugging in the USB-C monitor directly to my MacBook Pro M1 Max, and still no go.
** In that Dock, I have an external USB HD connected, as well as other USB components, and if the monitors don't come into play, the drives do not show up either, so nothing is recongnized.
A few things that work, and a tentative solution until Apple resolves this issue. Plugging the monitor directly into the MacBook Pro M1's HDMI port works flawlessly. Additionally, for me, rebooting the Mac resolves the issue until I perform the above step, which is unplugging, which I do because I work at different locations.
I'm not an Engineer, nor do I play one on the Internet, but somehow the signal that checks if something is connected to USB after waking from sleep has a hiccup in it. The issue only occurs when I remove the USB-C cable, use the computer, and then reinsert it into the system.
Oh, before someone asks, I've tried all three of the USB-C connectors on my MacBook Pro. I've tried it without the Dock, and I have also tried it with other monitors I have connected to my other Mac in my home office. This issue occurs only on my MacBook Pro and only when I switch from clamshell (or open) mode to using only the laptop screen, then back to the external monitors. (And as I said, my bandaid fix is to reboot, but what a pain in the you know where)
Now that I can reproduce it, I'm writing up a bug report for Apple. Good luck, everyone!
So, I actually finally figured out how to fix my issue tonight, and I'm almost embarrassed that it took me this long to think of it. Wavlink support tried their best, but I managed to figure this one out first:
Plugging in my MagSafe charger appears to completely break high speed thunderbolt connectivity. It will work for smaller things like mice and keyboard, but any kind of hub or display will just fail to establish a connection while I'm charging with the MagSafe port. Once I unplug the charger, the dock works great, and so does plugging my displays directly into the laptop.
I have no idea why this would be working fine and then break after an update. But my particular use case is fixed so I'm not going to worry about it too much at this point. So if your monitors and/or dock are busted after a recent update, just try unplugging the charger and see if that helps. If you're just using a passive device that won't charge the laptop though, that might still be a dealbreaker for you.
SOLVED by reducing the refresh rate
After upgrade to 26.1 my two displays connected via a docking station to the Mac mini didn't work anymore. When disconnecting one of the cables the other one started to work. Replacing cables didn't resolve the problem.
What did resolve it for me was the following:
So not sure what exactly has changed with the 26.1 release, but at least I can use the docking station again.
THIS WORKED THANK YOU!
External Monitor Not Detected After macOS 26 Upgrade
