Hey!
So it turns out I was being completely dense and hadn’t read the support pages properly. I hadn’t set up a page for the image posts to display as the front page.
All working now, and I can confirm that the Intagrate plugin (https://en-gb.www.ads-software.com/plugins/instagrate-to-wordpress/) works well with this theme. It seems you can set it up to generate posts with the correct Image format.
Thanks for your response!