I just purchased an M1 MacBook Air that I would like to attach to an external display. When I do so, the video quality is pretty terrible. It almost looks like the the output is being slightly scaled. However, I've verified from my monitor's OSD that it is outputting to the correct resolution as well as from MacOS. There isn't any oversampling or other scaling effects from the monitor (it's outputting 1:1). Just as a sanity check, I took a screenshot and it outputs the correct resolution and looks beautiful on another computer attached to the same display. I've tried various output cables (USB-C to DP and HDMI) and this doesn't seem to have any effect. I've read elsewhere that there can be some colorspace issues on Dell monitors in particular, but this isn't a Dell monitor and it really doesn't appear to be the issue.
M1 MacBook External Display Scaling
displaydisplayportresolution
Related Solutions
I have found the MacBooks to be rather flakey when it comes to multiple monitors. However, I have found that if you hit the option key while selecting the scale radio button you get more options for the 4k monitors.
Also unplugging the HDMI cable seemed to reset the Mac to recognize that the monitor supported more resolutions.
I bought one (the Dell P2415Q) so can offer the results...
Scaled options are:
1504x846, 1920x1080, 2304x1296, 2560x1440 and 3008x1692
That is to say, the macbook always outputs 3840x2160, 60Hz as far as the monitor is concerned. It just "looks like" those resolutions in terms of real-estate.
1920x1080 is the default, and other scaled resolutions are given with the warning that "Using a scaled resolution may affect performance".
eg.
Looks like 1920x1080:
Looks like 3008x1692:
Source: My MacBook Pro (Retina, 13-inch, Early 2015), running 10.10.4, 2.9 GHz Intel Core i5, Intel Iris Graphics 6100 1536 MB
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Best Answer
This problem has been there for a while and it is because of the PPI. I believe Retina displays just don't work well with Full HD resolutions. Try a 4k resolution external monitor and it should work fine.