Displaying large format 'card' images when sharing URLs to other platforms

Site URL: https://www.anne.health/

I'm a coding novice. What do I need to do so that whenever I share a URL from my website to another platform it displays the link image in a large format.

Currently when shared to Twitter and other adhoc platforms it only displays as a thumbnail image.

I know there needs to be some injection of code somewhere on the website which (when I've worked with other CMS) has applied this to the entire site.

What do I need to do?
What code do I need to insert?

Where (exactly) do I need to insert it?

Thanks forum - I asked Squarespace help, but got nowhere!