Problem:
The user is designing a content template for products, but the preview does not display data that it is expected to show in the respective blocks(image, title, price).
Solution:
While the user was designing the content template, he was using a post that is not a product.
After choosing to design the post with an actual product the data starts to appear in the preview.
The preview with dropdown is also a search box to change the current post used for preview. Check this screenshot https://prnt.sc/15ycbcp
The issue here is that the user wanted to edit a single custom field on their posts in a list without going to the post page itself.
Solution:
To resolve this you can create an edit post form and set it to submit using AJAX. Then removed all the fields that aren't needed leaving only the needed field and the submit button.
Finally just add that form to the view listing out your posts. From there you can Edit the Field A and change the values for each of the posts without having to go to the post itself. You can edit the fields from the list.