So, I might have my terminology wrong, but here's what I mean:
I currently have a 27" 4K monitor connected to my Mac.
It's 4K, so my actual resolution is 3840x2160.
However, in my System Settings, I have my effective resolution set to 2560x1440.
macOS automatically scales the interface to make text and elements more readable. A 4K monitor (3840x2160) scaled to 150% would appear as 2560x1440 with a dot pitch of about 163.18 PPI, resulting in a pretty sharp image. PPI is "pixels-per-inch" AKA "pixel density". The higher the PPI, the sharper the image.
If I had a 1440p monitor set to 1440p resolution, my PPI would be about 108 PPI, which is much less sharp than 163 PPI.
Caveat: All the stuff I said before about non-integer scaling.
I currently have a 27" 4K monitor connected to my Mac.
It's 4K, so my actual resolution is 3840x2160.
However, in my System Settings, I have my effective resolution set to 2560x1440.
macOS automatically scales the interface to make text and elements more readable. A 4K monitor (3840x2160) scaled to 150% would appear as 2560x1440 with a dot pitch of about 163.18 PPI, resulting in a pretty sharp image. PPI is "pixels-per-inch" AKA "pixel density". The higher the PPI, the sharper the image.
If I had a 1440p monitor set to 1440p resolution, my PPI would be about 108 PPI, which is much less sharp than 163 PPI.
Caveat: All the stuff I said before about non-integer scaling.
This is handy tool to explore PPI and monitor sizes: https://www.sven.de/dpi/