Overview of problem
Let's suppose we define a collection with the formula beneath.
Address1:"1 High Street", City:"London"
Next, we add an edit form and use the 'Data source' dropdown to set the data source to our collection (colAddresses).
If we now click the 'Edit fields' link, the 'Add field' button is grayed out, as shown in the screenshot beneath. This makes it impossible to create cards that based on the fields in the collection.
It's possible to add a custom card. However, the limitation of a custom card is that it does not expose an update property. As the screenshot beneath shows, the update property is missing from the card.