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

Example Figma Prototype URL

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

Scaling your Figma Prototype

For the best results, please ensure that the aspect ratio of the Figma layer you're embedding the prototype into matches the aspect ratio of your Figma Prototype, and ensure that the scaling mode is set to: scaling=scale-down-width

eg. https://www.figma.com/proto/g4gs9PlrdqPsHzX3n1cTg5/Dieter-Rams-Deck?type=design&scaling=scale-down-width