Select and click Stop Inheriting Permissions .
Navigate to your document library and select (gear icon) > Library settings . how to prevent download in sharepoint document library
To prevent downloads in a SharePoint document library, you can use several methods ranging from simple sharing link restrictions to advanced tenant-wide PowerShell policies. Select and click Stop Inheriting Permissions
The best approach depends on whether you want to restrict a single file, a specific group of users, or an entire site. 1. Restricted View Permission Level (Quickest for Groups) a specific group of users
Block File Downloads Using Custom Permission Levels in SharePoint
The "Restricted View" permission is a built-in level that allows users to view files in the browser but removes the ability to download, print, or sync them.