How to embed an iFrame from Google Slides
Roles: Authors, Collection Owners
Click 'File' and then 'Publish to the Web.' Make sure that you uncheck 'Require users to sign-in with their account" if it is selected. NOTE: Publishing to Web will not surface your document in any search results in the web since the doc is being published to a private site - Guru.
Click 'Embed'. Copy the entire Embed field.
In the Guru Card, click the "Markdown" icon (box with a pen) in the editing bar.
Paste the copied 'Embed' code into the Markdown box
Paste that directly into a new line on a Guru card. The presentation will appear.
Drag the shaded bar at the bottom of the card to adjust its size.