Scaling on external monitors with MBA 2025 M4

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Scaling on external monitors with MBA 2025 M4

Hi. I'm in the process of migrating from a 2019 Intel MacBook Pro to a 2025 MacBook Air M4 and something strange is happening with my external monitor setup.

I've had the MBP connected to two external 27in monitors: a 2019 LG 4G display connected via a HDMI to USB-C adapter, and a 27in QHD display that's a couple of months old, connected via USB-C. Both were working fine at 2650x1440 resolution with the MBP, but when I try to connect the same kit to the new MBA, the LG monitor is behaving strangely.

It'll run happily at 3840x2160, but everything on screen is too small for comfort. At 2650x1440, items on screen are now fuzzy. If I choose 1920x1080 HiDPI, things are sharp again, but now too large. Yet if I plug the cable back into the old MBP, 2650x1440 works just fine and windows are roughly the same size as they are on the built-in screen.

I can't work out what's going on. The LG monitor's native logical resolution is 2650x1440, yet it's acting like it's scaling (badly) when the MBA tries to drive it at this resolution. But the old MBP has no problem doing so. Does anyone have any suggestions as to what could be causing this? I'm wondering if my USB to HDMI adapter isn't playing nicely with the TB ports on the new MBA - but before I splash out on a new one, could there be something else going on?

Thanks in advance....

MacBook Air 15″, macOS 26.0

Posted on Oct 2, 2025 9:37 AM

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Answer 1

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JamesT06 Author

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4 points

Oct 3, 2025 10:57 AM in response to Grant Bennet-Alder

Thanks Grant. I've marked this as helpful as I suspect it's useful advice for others who may find this thread. In my instance it didn't fix the problem, as when I turned off the 'show resolutions list' option in order to try to create the view you've shown above, it only worked for the built in display - the external monitors still presented a list, but 2560x1440 resolution wasn't even offered as an option. My MBA was still convinced that the 4K monitor topped out at 1080p. I may have been missing something that would have generated the view above for these monitors, but in the end something else came to the rescue:

For reference for anyone searching for a similar solution: what did work was swapping out the USB-C to HDMI adapter for a dedicated TB4 dock. As soon as I switched it on, both displays are now running super-crispy 2560x1440.

My non-expert takeaway is that there may be some old USB-C display adapters like this that just don't play nicely with the TB4 ports on a new MacBook Air.

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Answer 2

Oct 3, 2025 3:10 PM in response to JamesT06

first, be certain you are not Mirroring the internal display. When mirroring is enabled, BOTH displays Run at a compromise resolution, in exact lockstep, using the same display generator for both.

next do not show all resolutions to be set manually. use THIS:

[Edited by Moderator]

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Answer 3

Oct 3, 2025 3:06 PM in response to JamesT06

<< As soon as I switched it on, both displays are now running super-crispy 2560x1440. >>

Graphics are rendered at full native resolution of Your Hi-DPI displays. Text is rendered at a larger size, then scaled down to a "looks like" resolution of 2560 by 1440, but very sharp as you point out.

If your display is not detected as capable of higher-than-2K native resolution, the resolution saying will not be offered.

In your case, it is possible that adapter was limiting the apparent resolution to lower numbers.

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Scaling on external monitors with MBA 2025 M4

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