While true, the ppi increase from most 4k screens would not be as large as the Apple Studio Display.
Most 4k monitors are 24 inches, and those monitors will be 192.94 ppi. [0][1] The Apple Studio Display comes in at 218 ppi. [2]
Where are you getting this? I was looking at monitors recently and it's impossible to find ANY 24" 4K monitors. Most of them are 27", which at that screen size you really need scaling. My LG 27" 4K recently went out so I downgraded to my older 1440p 27" monitor. I'm not using scaling anymore, but the text doesn't have that buttery smooth look...
It's even worse than I thought!
https://www.bestbuy.com/site/searchpage.jsp?st=4k+monitor+24...
https://www.apple.com/shop/product/HMUA2VC/A/lg-ultrafine-4k...
There appears to be exactly one 24" 4K display being sold. Which is more a niche than a good number.
My theory is that most people, for all practical purposes, are blind.
So at 24” 4K does everything looks nice and smooth without scaling like a built in Retina display?
I spend most of my day watching a screen, and I want it to be perfect. Because of this, I would be tempted to buy the new Apple display. However, buying an iMac makes much more economic sense. I have no idea why display manufacturers can't get the details right.
Windows and Gnome look gorgeous at 2x rendering. macOS does too, but that's expected.
I'm sitting in front of a 4k 27" and the 160ppi is almost indistinguishable to my macbook at 227 due to the different viewing distance.
And I always had the impression most 4k displays were 27".
I don't even use HDR, the density is just that good for looking at text all day. It takes on this milky quality that I haven't seen on any other monitor before this.
The complete lack of appreciable IPS glow or uniformity issues is also better than you might expect for text. Especially with dark backgrounds which will now present one impressively uniform block of color, improving contrast.
> most 4k displays were 27".
This is in the direction of lower PPI/DPI, which is worse. That is:
4K @ 24" > 4K @ 27"
Also, as others have noted, the Apple Studio Display is 5K, so more UI is visible than on a 4K monitor.
Personally I would much rather that they made the display 4K and 120hz instead of 5k and 60hz. At that size, I don't see a big difference between 4K and 5k, but the 60hz vs. 120hz jump is very noticeable.
Obviously there are people who need the higher PPI, but if you look at text all day I'd recommend giving 4k a try before spending 3-4x as much on a 5k. You can run the 4k display at 5k, the same way that you can run a MacBook Air at 2880x1800 even though it's really 2560x1600. Modern scaling algorithms are very good.