Hi Shmulik, 

Welcome to the Box Community!

When a Box user opens a file in their Box account using Excel online integration, Box sends the file to be opened to Microsoft platform. However, to insure stability and functionality between both partners (Box and Microsoft) MSFT controls what functionality and features is available in the editor that is provisioned by Microsoft online. We don't have full control over the functionality and features offered. Thus, some functionality, such as "Show changes" is unavailable to the integration editors.

We recommend reaching out to Microsoft Support for further questions and assistance on using this function.

Thanks for posting and please let us know if you have any question!

Hi, when you create an excell from MS Online Show changes is available, it is only document created or uploaded and stored in box for which show changes is not available. Please help as this release is not true without "Show Changes" available when document stored on box.
https://blog.box.com/new-ways-to-work-box-office