Hi @Zolotoy
By hiding do you mean the collapse action or complete hiding? According to my test, when you export the report to EXCEL, if you perform the collapse action, then excel can expand the hidden items, if you completely hide, then excel will not retain the hidden columns.
For more details about hide an Item, you can refer to this link: https://learn.microsoft.com/en-us/sql/reporting-services/report-builder/hide-an-item-report-builder-and-ssrs?view=sql-server-ver16.
Best regards,
Aniya