Hello Fede,
To use it dynamically, you can just insert this {{dc:post:meta post="post_id" key="instagram"}}
. This will ensure that it will always display whatever is added in the Instagram custom field of the current post that you are viewing. Just make sure that your post meta key is correct or it will not display anything.
I also check your custom field and as it turns out, it will output like this: <a href="https://instagram.com/laguiaveg" target="_blank" rel="noopener noreferrer">instagram.com/laguiaveg</a>
which means that you cannot use the dynamic content {{dc:post:meta post="post_id" key="instagram"}}
as the link in your Button element.
You can test it out by adding a Text element and insert this:
<p><strong><span style="font-family: futura-medium;">Instagram:</span></strong> [field "instagram"]</p>
To get this resolve, please edit your custom field settings and make sure that whatever you insert in the field will be the same output and not a generated link as the output.
Hope this makes sense.