For machines that don't need to mix scaling this is pretty much a solved problem - I've run Windows at 125%, Linux/Cinnamon at 150% and OS X at ~150% and they've all preformed just fine for coding tasks.
The only mess is if you have mixed displays - and even that is mostly still problem only on Linux.
It works with non-Apple displays (I use a Dell 4K monitor with my Mac Mini), but the OS has to be able to detect that the pixel density is suitable. It’s possible that macOS can’t discern enough about your monitor.
If you option-click on the resolution options you may be able to manually override it.
Careful with that setting. Any non-integer scaling like 1.5x will force macOS to render everything in 5K (I think?) and scale it down to the target resolution - this is way more taxing on GPU, battery life etc. than 2x scaling which simply display all content twice as large (everything is delivered with 2x assets after all).
I actually don't use HiDPI on my 4k 27" monitor. Instead in Accessibility Settings I turn on Large Text (Linux Mint), which is like 1.5x or 2.x font sizes. All icons I can see quite well as they grow too, but whitespace is minimized, so I get a lot more screen real estate and it would fool others. It looks like HiDPI.
The only problem with this approach is the mouse cursor stays tiny, and it doesn't have the OSX shake option to find it, though I rarely lose it so it isn't much of a problem.
If you aren't able to configure it, you get just get microscopic text (unless you're using something like a 55" tv as your monitor)