I cannot tell you how very many new shops I look at which have useless, non working, social media links. I often click them and at least 50% go nowhere because the links they have entered are incomplete.
I just had a look at the setup page and it is indeed not at all clear. A little bit of helpful text might be added perhaps ( @Folksyadmin ?)
Instagram Facebook Pinterest all require the relevant site prefix before your user id. Twitter/X does not.
So here is an example of what you need in order for those links to work because to be quite honest I would never buy from a shop which had not taken the trouble to check that the links from their shop front actually worked as i would take that as a lack of attention to detail. And attention to detail is pretty important when buying handmade.
