In previous versions of SSRS there is no way to hide the Download menu from the SSRS Portal which allows users to download Report Builder, Mobile Report Publisher applications. Normally Enterprises don’t want their users to download software and install in their laptops instead they normally push via Group Policy (GPO).
In SSRS 2017, now you can hide the Download menu on SSRS Portal by connecting to the SSRS instance using SSMS and right-click on the SSRS instance and select Properties and click on Advanced and set Show Download Menu as false.
Note: There is no need to restart the Report Server instance after the change.
As shown in the above screenshot, no Download Menu appears now.