HiDPI on Linux is certainly not as good as MacOS (from what I've heard) or Windows but it can be decent. If you are on Wayland than display scaling both integer and fractional works pretty well. Scaling older X11/Xwayland applications can be a bit of a pain so sometimes those windows look blurry.
4K itself without any scaling works perfectly fine so I typically try to get laptops and monitors with a DPI between 100 and 140 so that I don't have to worry about scaling. Higher resolutions on smaller screens i.e laptops also use more power anyway.
I currently use a 4K monitor and a 2K monitor side by side for my work with 1.5x scaling on the 4K monitor, so things are the same size on both. Gnome only allowed integer scaling by default, but IIRC I enabled fractional scaling with a dconf setting that I found through googling. I don't have any issues with this setup, although obviously things look more clear on the 4K monitor, so some people might not like the disparity.
Thanks for sharing. I run my 4k monitor at home at 1:1 so I don't use (and don't need) scaling, but nice to hear someone else had some experience with it. I always worry about the lag on desktop features with Linux, but I've generally not had problems in recent years with Fedora, for example.
On my 2013 Google Chromebook Pixel (running real Linux) I set Xft.dpi: 240 in my .Xresources file, matching the screen resolution. Seems to work well. I’m not sure what “scaling” is. Is that it? I wouldn’t want to use a 140 dpi screen, unless it were a big one mounted 6 feet or so away.
4K itself without any scaling works perfectly fine so I typically try to get laptops and monitors with a DPI between 100 and 140 so that I don't have to worry about scaling. Higher resolutions on smaller screens i.e laptops also use more power anyway.