Blackmagic camera app and disk space

Please do you know why doesn't the Black Magic app provide the same storage capacity as the iPhone's information?

[Peter Chamberlain]

We make available all the API offers to us.

Sorry Peter, I'm not an expert, so I probably expressed myself poorly. What I meant was that the available storage space displayed by the application is significantly lower than that indicated by the iPhone, as you can see in the attached image. Could the iOS operating system be blocking a portion of the disk space, making it inaccessible to applications?