You can restore the tabbed views in the Project Browser of Revit 2025 by following these steps:
Open the Project Browser by clicking on the View tab, then the Windows panel, and selecting User Interface drop-down to make sure the Project Browser is visible.
If the tabbed views are still not visible, you may want to ensure that your interface settings have not been altered. You can check this by resetting your user interface settings.
If available, you can use the ResetUI utility to reset the interface settings. Download and run the ResetUI batch file specific to Revit 2025:
Close Revit.
Download the ResetUI utility.
Extract and run the BAT file for Revit 2025 (make sure to backup necessary settings or configurations before doing this as it resets the settings to default).
Following these steps, you can restore the default tabbed views in your Project Browser. Consulting Autodesk Support or help documentation might provide more tailored solutions if issues persist.
RVT to the max