The Fonts add-on adds Styles and Sizes drop-down menus to the WordPress visual editor. Styles gives access to the available style choices, while Sizes offers additional text sizes. Fonts Pro is the paid upgrade for adding a selection of Google and custom fonts, including premium fonts, to the editor.

Choose fonts while editing

After configuring your font selection in the Fonts Pro settings, pick from those fonts while preparing a page or post. The Styles and Sizes menus remain available for their separate formatting choices.

1. Install the Fonts add-on and upgrade to Fonts Pro.
2. Use the Fonts Pro settings to add the Google, custom, or premium fonts you want to use.
3. Open the WordPress editor for your content and select from the configured fonts and available style and size choices.

Fonts Pro includes Gutenberg support. The product listing describes it as working with the latest version of Gutenberg.