I can see you are using a child theme on your site, so you could bundle your custom font into the child theme.
Other ways inlcude using a custom font plugin that allows you to upload your own fonts.
The fonts won’t show up in “customize/typography” as this is a defined list of Google fonts in the theme.
Is your custom font a Google font, a saved font that you have on your computer, or something else?
If it is a Google font, we may be able to add it to the the theme’s list of Google fonts, and then it would be selectable in “customize/typography”.