The question is answered, right answer was accepted.
Also consider submitting this as a feature request, directly to Squarespace so they know it's something that you're looking for: https://support.squarespace.com/hc/en-us/requests/new
Currently, if you include an excerpt with a post in the Five template, the post will be shortened on the main blog view, with a "Read More" link below the excerpt. The only way to prevent this behaviour is to remove the excerpt completely.
I'd like the ability to have an excerpt for convenient cross-posting to a Facebook page, but without shortening posts on the main blog page. Is there a way to do this with custom CSS?
Currently, my workaround is to create the post with an excerpt so that it cross-posts to Facebook correctly, then reload the page, edit the post, and remove the excerpt. Suffice to say it's not a very elegant solution.
This question has already been asked before here, but it's old and doesn't really have an answer so I figured I'd create a new question (apologies if this is considered bad form).
Answer by Jeng · Aug 11, 2016 at 04:26 PM
You might be able to use the code from this thread to do this: https://answers.squarespace.com/questions/32694/always-display-full-blog-post-not-excerpts-except-in-summary-block.html
Answer by JonathanGennick · Jan 21, 2014 at 07:56 AM
There's a handy work-around for pages in that you can inject Open Graph tags directly into a page header, allowing you to specify precisely what is picked up by Facebook. I blogged about that recently. However, the technique cannot be applied to blog posts.
The presence of an excerpt is the flag that Squarespace relies upon to decide whether to show a post in its entirety. I don't know of any work-around that will help in your situation.
I use Five for one site that I manage. I ran into a related issue the other day in that the display of thumbnails is also controlled by the presence of an excerpt. So I kind of feel your pain. I had to compromise on what I wanted. Sometimes we just have to live with how the platform is designed.