In 2013 I bought a Macbook Pro 13” which came with a HiDPI display (also known as retina display). Already back then the support for a single HiDPI display was quite alright with KDE4 and a few tweaks here and there. Months later Qt5 got native HiDPI support and most applications switched from GTK2 to GTK3 and finally the outliers (chromium based apps, godot, arduino…) got support for higher DPIs as well.