I’m using the last version of Gp premium and can’t get fonts to change. I tried with the customizer and tried also with CSS code. The problem seems to happen only inside posts. If I manually change widgets title font (for example), it works on custom pages, but not in post pages.
I can see a lot of warnings in the developers console related to a font being blocked.
This looks like a custom font that is being requested from a HTTP url – which needs to be a HTTPS url.