Folders with imported files on iPad not accessible

We are using shapr3d for iPad with our students, and for data security reasons we cannot use iCloud. I do not find a way to import parts like screws (.step): I can store .step-files in the downloads folder and copy them also to the shapr3d folder. But when selecting “import” in a design shapr3D only offers pages folder (why???) and the Nextcloud folder on my device. How to get access to the .step file?

(Our devices are managed with Mdm “Relution”, but we didn’t apply any restrictions concerning the folders)

Shapr3d on iPadOS 15.7, all iPad versions