Is there a report that shows the available archive for all cameras per date and time or report showing the size on disk of the archive per camera? If not, can this be done via the SDK?
No, there is no functionality in the XProtect Professional for this.
The MIP SDK would not be able to get the information from the XProtect server as the server does not have the functionality. As a workaround it might be possible programmatically (not using MIP SDK functionality) to explore disk usage.