When creating an invoice with multiple items, those items will also be presented in the report as part of a single invoice or bill, lanuk5.
Since it is showing duplicate on your end, I suggest clearing your browser's cache so the system can start fresh. Also, ensure that you're using a supported browser to avoid any unusual system behavior.
After that, let's rerun the reports to customize and choose the correct filters to prevent duplicate data issues. See this page for your guide: Customize your reports with a modern view.
Feel free to add your comment below if you need more guidance about reporting concerns in QBO.