Hi Fraser Paterson,
Thank you for reaching out to Microsoft Community.
Pre-installed software, apps and updates use a significant amount of the internal disk space of your Surface Pro 7. For the Surface Pro 7 with 256GB SSD and 8GB RAM, the available disk space will be around 205GB (Surface storage options and hard drive sizes). When you first got the Surface and before you downloaded your photos and files, were you able to check how much disk space is available?
You may also go to Windows Settings > System > Storage. Click This PC (C:) then you'll see the details of what are those contents that is taking up the space on your SSD.
If this answer your question, we highly encourage you to inform our Community by clicking on Yes or marking my post as an answer. This will help other members who may have the same issue as you. Otherwise, don't hesitate to update us so we can further assist you.
Kind Regards,
Marrion Y.