It all begins with 4K monitors
HiDPI (4K or higher) monitors, standalone or part of a laptop, are fun to use but this fun is corrupted often either on the application level or even the system level, e.g., Java as the one instance being responsible for the execution of Java applications and thus being an important part of the system as a whole.
In addition, components such as libraries can take the complexity of the problem to an even higher level. You'll be lucky if your application of interest is a jar which can be launched using the uiScale option. This helps in some cases, but really only in some. But other applications like the notorious Eclipse IDE cannot be scaled to a reasonable appearance without severe side-effects. If you scale it by a factor of 2, the icons in the object tree are displayed incorrectly and are cut in half.
Most interestingly, the HiDPI problem is equally bad on Windows as well as on Linux systems. Either way you have to fight yourself through legions of real or, in most cases, pseudo-solutions. And in the end, you'll often give up without having come to a solution.
Sometimes I think, 4K displays are not what the world really wanted, the nerds using them will find out how useless they are. Okay, that's a bit over the top, but the hassle you sometimes have using wrongly behaving applications is over the top also.
Software causing trouble in my case
I have these candidates on my list:
If I hadn't already two 4K laptops, instead I'd rather buy two Full-HD machines together with two Full-HD monitors for each of one. Okay, the problem is the footprint on my desks, but the footprint on my mental condition would be much less.
I don't want to be unfair to the developers: if you start using a certain programming language you deal with a plethora of intertwined dependencies, think of plug-ins, libraries and so on. And when you start developing using QT for example, you have a monster of a software djungle to cope with. So, up to a certain degree I understand when a developer explains, that he can't do anything about it and has to wait for a solution by the QT team. But what about them? They are happy as long as the product is profitable, right? And so are the others in the production chain? Again, the end-users are the idiots. With respect to Java I found out, that there are solutions to mitigate the problem at least but the programmer has to do some extra work, not much, but a bit. But even this seems to be too much. Thank you.
A Technical Footnote
Technically you may come into trouble with DPI/HiDPI problems if you set your system's DPI value to something different from the system's default. I've published a blog article about Google Chrome which showed blurry maps (www.kolloquia.com/blog-english/google-chrome-has-problems-displaying-google-maps). This phenomen was caused by an altered DPI value on a screen which wasn't even Full HD.