In admin site setting you can change the font to Montserrat.
base font
heading font
If you want to add a font which is not in core but it is in Google Fonts then you can use this theme component:
In admin site setting you can change the font to Montserrat.
base font
heading font
If you want to add a font which is not in core but it is in Google Fonts then you can use this theme component: