Thanks for the reply Shoverian - building on your tips, there were a few more steps I had to work out to get this functional, so if it can save someone some time…
Strapi v4 no longer returns media data (to improve performance)
So to get the extra data you have to add this to the fetch :
?populate=*
and your planeitems (or currently storeitems in this tutorial) fetch becomes:
fetch("http://localhost:1337/api/storeitems?populate=*")
and to hook it up to the right url I ended up setting my imageLink to
imageLink: "http://localhost:1337"
and got the storeitem image url using
:src="imageLink + storeitem.attributes.image.data[0].attributes.url"
FWIW!