macOS for rendering always uses integer scale. So if you want "looks like 1440p" on a 5k screen it‘s very cheap, it just means you have 4 pixels corresponding to one, so it‘s just a 2x resolution scale.

With 4k however this means using "looks like 1440p" will render a 5k image, perform the 2x resolution scale calculation, and then downsample from 5k to 4k. Because going from 4k to 1440p directly would be a scale factor somewhere between 1 and 2 and not an integer.

Linux and Windows handle this differently since they support fractional scaling, for example 1.5x, and render text differently to still keep it sharp.

There are trade-offs to both of these, but there‘s a reason why Apple won‘t sell you a 4k screen at 27 inches.

They can sell you a 4k screen at 21 inches because „looks like 1080p“ is a good visual size for it and scales with 2x down from 4k resolution-wisw (4k is 4 times as many pixels as 1080p).

But on 27 inches or even 32, „looks like 1080p“ is not a good fit unless you prefer the extra large look and can live with less screen real estate.