macOS only properly supports ~110ppi and ~220ppi,
There's a big dose of "your mileage may vary" around this.
While there's no doubt that 220dpi (Apple 5k/6k displays) is the best, ~160dpi (i.e. "4k" UHD @27") is still very usable and definitely better than 110ppi. The "support" issue is really that system fonts, icons, dialogues etc. are designed for either 110 or 220ppi - so you get a choice between
tiny (using the 110ppi versions at 160ppi)
, rather chunky (using the 220ppi versions at 160ppi) or using a non-integer scaled mode to get them "just right" at the expense of a very slightly "soft" result (you're getting 5k downsampled to 4k) and extra GPU load (an M1 or better shouldn't break a sweat).
Opinion seems to vary between "non-integer scaled mode will make your eyes bleed" and "just stop climbing up on the desk with a jeweller's loupe and doing A/B comparisons with a display that costs 3x as much". I incline towards the latter.
Plus - it's mainly about dialogues, menus etc. since virtually every creative application allows you to freely zoom the
content (or set font sizes in code editors etc.) and even a 160ppi screen will give you a lot more detail/clearly render smaller text than a 110ppi one.
I'm currently trying out a Huawei Mateview with a view to replacing my iMac with a Mini or Studio driving a
pair of MateViews. This is a 3840x
2560, 3:2, 28.3" screen with Mac mini/studio-esque styling. So it's effectively the same width as a 27" 16:9 screen, but with another 2.5" of vertical height and the same ppi as a 27" 4k UHD screen. I find the extra height partly counteracts the larger system fonts/menus/icons making it very usable in 2:1 mode. Is it in the same league as the 5k iMac/Studio Display? Not quite - but it's pretty good and you can buy 4 for the price of a Studio Display. May not be available in some countries because reasons that belong in another forum.