Hi there,
theres no simple way of adding a Customizer option for the Blockquote.
It would require some CSS like so:
blockquote {
font-family: arial;
}
You can change arial to any font you want – if it is a font that is already chosen in the Customizer > Typography settings then you need to do no more.
If you want a different font then you would need embed that font.
Go to fonts.google.com
Select the Font and then the Style you want. In the sidebar it will provide you with the Link you can copy this and add it to a Hook Element:
https://docs.generatepress.com/article/hooks-element-overview/
Select the wp_head hook
And set the Display Rules for where you want the font to load. eg. Posts > All Posts.
Fonts.google also provides you the CSS font-family property for that specific font.