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Custom master pages are currently not supported for "modern" pages. Documentation: Supported customizations for "modern" pages Similar thread: Customize master page on modern/communication site


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You need to append the &action=embedview query string parameter instead of &action=edit in the file URL. So your file URL should be like: https://<tenant>.sharepoint.com/:p:/r/sites/<siteName>/_layouts/15/Doc.aspx?sourcedoc=%7BC021A4AD-66A0-4505-A5CA-9984B810FE67%7D&action=embedview


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The user appears to have set their Microsoft 365 theme to "High Contrast". The user can change this back to your company theme by going to Delve > clicking the cog > and choosing their company theme under "Themes".


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