To embed an interactive version of your Framer X design into an Avion user story, you need to generate a live preview link. You can do this by clicking the mobile icon — this can be found on the right at the top.
Then click Start.
Then open up the preview in a browser.
Finally, copy the link from your browser's URL bar.
This link can be pasted into your user stories in Avion under the Attachments menu. Avion will recognise this as a Framer X link and give you an interactive embed. This will stay up-to-date as you change your designs, as long as the link remains visible to Avion.