You can embed a Figma design by clicking the Share button in Figma, with Anyone with the link set to can view, and then click the Copy link button to get your Figma URL, then pasting the URL into a Pitchdeck layer’s Embed input field.

Example Figma Design URL

https://www.figma.com/file/g4gs9PlrdqPsHzX3n1cTg5/Dieter-Rams-Deck