PMurphy wrote:
Easiest way to show what I mean... here are the M3Pro options (3200x1800 is one) and then the M4Plain options
That's very odd.
In Retina scaling modes, the internal drawing canvas has twice as many pixels in each direction as the nominal Displays Settings ("UI looks like") resolution. For Retina "looks like 3200x1800" mode, the internal canvas has 6400x3600 pixels – it has a higher resolution than the native resolution of a 32" Apple 6K Pro Display XDR.
Thus if you were attaching two monitors to a M3 MacBook Air (which has a resolution limit of 6K on the always-available output, and of 5K on the "lid closed" one), Retina "like 3200x1800" mode would not be available on the "lid closed monitor." There is at least one report from a M3 MacBook Air user, on these forums, for which this is the most logical explanation.
In your case, the display specifications of the M3 Pro MBPs and the plain M4 MBP are virtually the same. Note the key "up to 6K resolution" phrase in both sets of Technical Specifications.
Which versions of macOS are you running on the M3 Pro MBP and on the plain M4 MBP? Is it possible that this is a macOS thing, with Apple having moved the 3200x1800 option to the "Show all resolutions" list – or maybe even having removed it altogether?
MacBook Pro (14-inch, M3 Pro or M3 Max, Nov 2023) - Technical Specifications - Apple Support
MacBook Pro (16-inch, Nov 2023) - Tech Specs - Apple Support
M3 Pro
Simultaneously supports full native resolution on the built-in display at 1 billion colors and:
- Up to two external displays with up to 6K resolution at 60Hz over Thunderbolt, or one external display with up to 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI
- One external display supported at 8K resolution at 60Hz or one external display at 4K resolution at 240Hz over HDMI
MacBook Pro (14-inch, M4, 2024) - Tech Specs - Apple Support
Simultaneously supports full native resolution on the built-in display at 1 billion colors and:
- Up to two external displays with up to 6K resolution at 60Hz over Thunderbolt, or one external display with up to 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI
- One external display supported at 8K resolution at 60Hz or one external display at 4K resolution at 240Hz over HDMI