The File Reader web part is used to read documents with the tracker. The web part has a simple view option. This forces the document into the embedded reader than than the Office online editor. To change the option, edit the page to update the web part properties.
All documents and files to be tracked must be opened using the File Reader page (/SitePages/CTFiles/File-Reader). This is the native page used by My Reads.
Files viewed without the File Reader page will not be tracked.
Hidden Tracker content must be displayed in My Reads or using the PnP Modern Search web part for tracking to take place.