It is called 'Zoom Box' and is <Command ID="RoamerGUI_OM_MODE_ZOOM_BOX"> in RoamerCommands.xml. The default shortcut is Ctrl-5 or you can also access it by right-clicking in model space>Viewpoint>Navigation Mode>Zoom Box. It acts differently than 'Zoom Window' found on the Viewpoint>Navigate panel or on the Navigation toolbar which is <Command ID="RoamerGUI_AutoCAM_Zoom_Window"> in RoamerCommands.xml in that the middle mouse action you describe is only on Zoom Box not Zoom Window.
I don't have 2025 installed, but it is the same in 2022 and 2024. You can rebind the shortcut in RoamerCommands.xml found in C:\Program Files\Autodesk\Navisworks Manage 2024\Layout