Different external display resolution after MacBook Pro upgrade

in Retina scaling modes, the Mac draws on an internal canvas that has twice as many pixels as the nominal Displays Settings resolution in each direction.

So Retina “like 1920x1080” draws at 4K detail. Retina “like 3008x1692” draws at a 6K level of detail, then downscales the picture to fit on the 4K display.

Retina “like 3360x1890” would involve drawing at a greater than 6K level of detail. I don’t know whether the plain M5 chip supports that or not.

<< Why should I choose that one when I want a different resolution? >>

On modern Macs that have the ability to scale the text you see, best results are obtained by using the full native resolution, and having the Mac scale the text (ONLY) for preferred legibility.

In general, poorer results will be obtained by changing the resolution of the entire display. That is why I recommended using Mac Scaling feature instead of manually adjusting resolution.

¿Do you have a need for setting a a manual resolution? if so, please explain -- there are some other solutions that might be able to solve certain issue with resolutions.

but if you have a compelling reason to scale the display resolution

When you have a display whose native resolution is higher than 2K 2560 by 1920, you should turn OFF 'show all resolutions' and use this alternate one that should come up instead:

Re: “Both happily run the maximum resolution of 3840 x 2160 without difficulty“

If the display has a LCD panel resolution of 3840 x 2160, the 3840 x 2160 selection in Displays Settings will not select a Retina mode. The internal drawing canvas will have 3840 x 2160 pixels - instead of the 6720 x 3780 pixels that would be required for Retina “like 3360 x 1890” mode.

In other words, the 3840 x 2160 setting only requires pushing around about 1/3rd as many pixels, internally, as your desired setting.

Re: “Which is interesting but doesn't get me closer to answering my question: how to get my new M5 to use the same resolution as my old Intel.”

There is no guarantee that there is an answer that you want to hear. What if it turns out that the hardware in the plain M5 chip simply doesn’t support Retina “like 3360 x 1890 mode? That a 6720 x 3780 canvas is, for this chip, a bridge too far?

I don’t know that this is the case, but I can’t rule it out, either. Especially if you have set Displays Settings to show all resolutions, as a list, and the desired Retina mode is not there.

Re: “As an unrelated aside, since 26.0 System Settings > Displays reports the default resolution as being 1920 x 1080 on both machines”

It is probably showing you “UI looks like” resolutions, not the native LCD panel resolution. System Information will show you both the “UI looks like” resolution and the resolution of the internal drawing canvas, but even it may not show you native LCD panel resolution.

Re: “I'm sorry but I don't know what a UI looks like resolution is”

That is the term that System Information uses for the Displays Settings “resolution”, unless things have changed in Tahoe.

Retina-aware applications size text and objects as though the display only has that many pixels. Then, if the display is in a Retina scaling mode, they draw things in finer detail using the internal canvas resolution.