Or if you want a 27' display, then get either a 2560x1440 display (108 ppi, within standard range) or a 5K display (217 ppi, within Retina). That's not quite Retina, but closer by enough to make a noticeable difference. So I would say that if you specifically want 4K resolution, get at most a 24' display, which is 183 ppi.

As you might expect, that doesn't look as good as rendering for the target display pixel density in the first place, but macOS won't render natively for 163 ppi, and that post-render scaling can introduce artifacts that will be especially noticeable on text. It's true that macOS does offer 'Scaled' options to address these middle ground cases, but that involves rendering an image meant for either a standard or Retina display and then using post-render GPU scaling to blow up or shrink down that rendered image. If macOS treats it as Retina, then things will look LARGER than they should, and thus reduce your effectively available workspace. If macOS treats this display as standard, then on-screen elements will look much smaller than intended, and probably smaller than will be comfortable to use. A 27' 4K display results in a pixel density of 163 ppi, which falls right between the two types of displays that Apple designs for, and therefore makes it an equally bad fit with both of the available options. The reason is that Apple designs macOS for two categories of displays: standard (100-110 pixels per inch) and Retina (200-220 ppi). I would very strongly advise against using any 27' 4K display on any macOS-based system.

2560x1440 on 4k monitor mac os