Since the last update (21A5534d), my MacBook doesn't detect my 2nd display. I've tried swapping the display with a new one and trying different connection methods. My MacBook's built-in display goes black for a moment when I attach the cable, but nothing else happens.
I seem to remember that the System Preferences > Displays used to have an option for manually detecting a display, but it doesn't appear to be there any more.
I hope I'm not the only person experiencing this.
I know this post is over 2 years old, but I found it while searching for a similar problem. The monitor showed in display settings but the screen was black. Toggled around with the different settings and when I changed the refresh rate from 155 Herts to 120 Hertz the monitor worked.
Hope this helps someone :)
As of the Feb 6th, trying to connect 2nd monitor over USB C, it still an issue even with a Macbook Pro M2 Pro running on Sonoma 14.3 (23D56). Apple, this is a big issue, please fix it!!!!
I can't believe the problem can't be solved. This is ridiculous. Apple is a regret.
So I just got another monitor to setup next to my first so I can have a faster process for my editing. I have been recking by brain as an IT nerd of 30 plus years, as to why I could not get this monitor to work on my MacBook Air! Now I see it is not just me! I hope this is resolved soon, I do not want to go back to my Lenvo!
I'm still having the above issue. The solution posted above used to work for me, although I couldn't leave the monitor plugged in and unattended, becasue when it went to sleep it crashed both monitor and imac upon sleeping. then I'd need to reboot. But now in 2024, it's dead as a dodo. I cannot afford to upgrade my imac, and shouldn't have to as its working fine as a standalone computer. Does anyone have a new solution?
Here's what resolved this for me: plug in the lower hz monitor first.
I have two external monitors I use with my M2 Macbook Pro 16" (along with the Macbook display itself):
Both are plugged into USB-C/Thunderbolt 4. TB4 only has so much bandwidth, so it is unable to run both external 4k monitors at their highest 60/240 hz refresh rates.
However, there is enough banwidth to run them at 60 hz and 120 hz. The problem is, if I first connect the 240 hz display, MacOS allocated bandwidth based on available resolutions and refresh rates, the max being 4k/240 hz. This consumes all available bandwidth, so plugging in a second monitor means the second monitor doesn't get any bandwidth, and thus no display signal.
MacOS does not re-negotiate available resolutions/refresh rates for displays with already-established connections.
The solution? First plug in the 4k/60 hz monitor, then the 4k/240 hz monitor. The second monitor will only get enough bandwidth to support up to 4k/120 hz, but now at least both monitors work.