When dragging the font scale slider, I get this error:

I'm guessing it's a locale thing, where the program espects a point to be used as the decimal spacer but a comma is used instead?

Have you tried setting it to 3.5 manually by double clicking on the box and typing?

Observable as of *.3.0+ versions no longer uses an in-game results screen. These changes are out for 1.19, and I'm currently working on backporting the changes to 1.18.