JoeRees

I don't have any solutions.
I'm not surprised that there may be unused Javascript files being loaded. SS is a general purpose web site editing tool. So although you may not use a particular feature SS may load up some files that others using a feature would need.
In a perfect world SS would only load what is needed for your site of course.
If you are pretty sure SS shouldn't be loading up certain files when you aren't using a feature then I suggest contacting customer support with your observations. I think SS is interested in reducing load times. If enough people report a similar issue some action may be taken.

I don't see these being loaded for your site. I see the standard Squarespace scripts and the Shopify Buy Button script.
If you are seeing Facebook scripts, try your tests again in another browser or in private/incognito mode where extensions are disabled. If they persist, temporarily remove all code from your site and test it again. This will confirm whether your code is to blame. If the issue remains after all the code has been removed, contact Squarespace Customer Care.