I have Ubuntu 18.04LTS (with default Gnome and Cinnamon), my main display is 4K and external 1080p. I have problem with most apps. they don't scale properly on external display - they stay double size (2x) which makes them barely usable.
Apps that scale properly are: Gnome Terminal and Nemo (didn't test others/many).
How to solve it ? Apps that i use currently and auto-scaling would be really useful (chrome,chromium,intellij IDEA)