Based on your description, I understand that you want to share files with external users. As the same time, external users cannot edit files.
1.Enable external sharing in the tenant level. Go to SharePoint admin center -> Polices -> Sharing -> Set Anyone in the Content can be shared with section.
2.Enable external sharing in the tenant site level. Go to SharePoint admin center -> Sites -> Active sites -> Select the site -> Sharing -> Set Anyone in the External sharing.
3.Select file -> Share -> Anyone with the link -> Can view.
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