Many applications windows are scaled down to about two thirds of original size on my system (a laptop with two external monitors) and also on one another (also a laptop, but with a single external monitor).
For example, if I open a 1920×1080 PNG picture in Paint and maximize it on the middle monitor (that has native 1920×1080 resolution and is set to that resolution in Windows, with 100% scaling), the picture will not take up the entire window, but seems to be scaled down to about 66%.
What could be the cause and how to fix it?
It is Windows 10 Home 64 bit (up to date, version 1803).
The laptop monitor is 1920×1080 with 150% scaling and the third monitor is 3440×1440 at 100% scaling.
Logging out and back in does not help, neither does rebooting.
MS Paint showing own screenshot sized 1920×1080 but scaled down: