Custom text fonts

Hello there,

I've just started using MuseScore today and I can't find the answer to this question anywhere online. I can set a pre-installed font for my title and subtitle (like Segoe UI), but I can't set a custom installed one (like Open Sans, which I wanted to use). MuseScore just doesn't see them.
I've tried to set it up both through Inspector and also through Format -> Style, but nothing seems to be working. I'm using Windows 10, if that helps.

Thank you for your help!