Just installed Ubuntu 20.04 on a ThinkPad W451 where the screen resolution on the laptop is 2880x1620 and attached a second monitor with resolution 1920x1080. Sadly there seems Ubuntu either shows tiny fonts on the laptop monitor, or if the fonts on the laptop monitor are OK, the windows and fonts on the second monitor are huge.
In the Displays settings, there is a scale selection for either monitor, but the scale cannot be independently set: if I set it on one, it affects the other.
Is there a way to use dual monitors so that the font sizes would just adapt to the actual DPI for each monitor? I cannot believe that such a fundamental thing is still not solved in 2020: for each monitor, if we know the DPI, we should be able to draw things with the intended size. I tried this with the default window manager, xfce4 and Mate, and all of them get it wrong.