Here is what to do if the app does not appear as an option when you try to add it in the theme editor.
Check that your target template is supported. RuffRuff Author Profiles blocks are only available on the following templates:
Article template
Product template (Regular Plan)
Page template (Regular Plan)
Regular Plan blocks will not appear if you are not subscribed to the Regular Plan.
Go to "Theme settings" → "App embeds" in the theme editor.
If your theme is OS 2.0-compatible, use the App Block (added within a section) instead of the App Embed.
If none of the above applies, please contact customer support.