Hi @simonstjohn, welcome to the Supernotes Community!
If we break down the embed code, it has two parts – the iframe to display the card and the script to modify the height:
<iframe data-share-code="film+section+drive+test" src="https://my.supernotes.app/embed/film+section+drive+test?theme=hydrogen" style="width:100%;border:none;"></iframe>
<script>window.onmessage=e=>{e.data.hasOwnProperty('fh')&&(document.querySelector(`[data-share-code='${e.data.sc}']`).height=e.data.fh)}</script>
It seems like you embedded the card correctly in your initial post, but the additional script that is required in order to modify the height of your card is not running by Squarespace – see if there’s a way to enable the running of scripts?
You can only embed one card at a time. Being able to publicly view a collection of cards is an upcoming feature called Public Collections.
In your second post, you mentioned the help topic – it was a bit out of date and I’ve just updated it! I hope that helps.