Got my M1 Pro MBP upgraded to an M4 Pro, and have discovered an odd limitation.
M1 Pro MBP didn't support >60 Hz displays. They just ran at 60 Hz. I have two >60 Hz displays. One 5k-by-2k 120 Hz that I connect via Thunderbolt, and one 4k 240 Hz that for my work laptop, I connected via the Thunderbolt-out port on the 5K display via a USB-C-to-8K-HDMI adapter. (So I only have to plug in one cable to the laptop.)
On the old work M1 Pro MBP, that worked fine. On my 2019 16" Intel MBP, that works fine. On my M1 Max Mac Studio, that works fine. Albeit limited to 60 Hz on both displays. Not a problem, when I want higher refresh rate, I use different connections for the two displays.
On my new M4 Pro MBP, it only ran the 5K. But it offered the full 120 Hz. I tried connecting the 4K display via multiple methods (via a USB-C speaker-dock that also has an HDMI port, direct to the MBP's HDMI port,) and it just wouldn't show up. I tried my portable 1080p USB-C display, and it wouldn't show up. I thought maybe there was something wrong with my new work laptop.
Then I disconnected the 5K-120 display, and it happily ran the 4K-240. At 4K-240 Hz. Plugged in the 5K, no-go. Only one of the two at a time.
Then I happened to try connecting my portable 1080p first. Then the 4K-240. And it worked. Dual displays! But the 4K only offered 120 Hz. Then, the lightbulb moment. I connected the 4K through the USB-C dock. That forced it to only 60 Hz max. Voila, the 5K display worked when plugged in - limited to 60 Hz.
So the problem appears to be that M4 Pro supports:
So I have to plug in a "supports two displays" display first, then when I plug in the second, it works, but is limited to the "two displays" spec.
Now to see if I can cajole my IT department into letting me upgrade to an M4 Max so I can natively support both displays at once. :-D (I doubt it.)
And if you're wondering why the M1s and Intel worked just fine - because they don't even support the >60 Hz modes, they happily support both displays at 60 Hz without conflict, since the fact that the displays can do more is irrelevant.
M1 Pro MBP didn't support >60 Hz displays. They just ran at 60 Hz. I have two >60 Hz displays. One 5k-by-2k 120 Hz that I connect via Thunderbolt, and one 4k 240 Hz that for my work laptop, I connected via the Thunderbolt-out port on the 5K display via a USB-C-to-8K-HDMI adapter. (So I only have to plug in one cable to the laptop.)
On the old work M1 Pro MBP, that worked fine. On my 2019 16" Intel MBP, that works fine. On my M1 Max Mac Studio, that works fine. Albeit limited to 60 Hz on both displays. Not a problem, when I want higher refresh rate, I use different connections for the two displays.
On my new M4 Pro MBP, it only ran the 5K. But it offered the full 120 Hz. I tried connecting the 4K display via multiple methods (via a USB-C speaker-dock that also has an HDMI port, direct to the MBP's HDMI port,) and it just wouldn't show up. I tried my portable 1080p USB-C display, and it wouldn't show up. I thought maybe there was something wrong with my new work laptop.
Then I disconnected the 5K-120 display, and it happily ran the 4K-240. At 4K-240 Hz. Plugged in the 5K, no-go. Only one of the two at a time.
Then I happened to try connecting my portable 1080p first. Then the 4K-240. And it worked. Dual displays! But the 4K only offered 120 Hz. Then, the lightbulb moment. I connected the 4K through the USB-C dock. That forced it to only 60 Hz max. Voila, the 5K display worked when plugged in - limited to 60 Hz.
So the problem appears to be that M4 Pro supports:
- One 8K display at 60 Hz or 4K display at 240 Hz. (Apparently 5K at 120 Hz falls into this bucket.)
or - Two 6K displays at 60 Hz or 4K displays at 144 Hz.
So I have to plug in a "supports two displays" display first, then when I plug in the second, it works, but is limited to the "two displays" spec.
Now to see if I can cajole my IT department into letting me upgrade to an M4 Max so I can natively support both displays at once. :-D (I doubt it.)
And if you're wondering why the M1s and Intel worked just fine - because they don't even support the >60 Hz modes, they happily support both displays at 60 Hz without conflict, since the fact that the displays can do more is irrelevant.
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