However i got confused of “Then add block-editor.css in your child theme, and include the @font-face CSS (and any other CSS you want to load in the editor).”
Where to add it? In the customizer > additional css?
in The GB Blocks > Typography settings, you will see a Field: Enter Font Name.
Type font Name in there, and make sure to switch the Google Font Toggle off.
I’ve set the H6 heading into Amiri font. It appears in the system stack in the typography setting (customizer), but somehow it was not showing in GB blocks.