That depends. If you would like to receive support (helpdesk, bug prioritization, new features), you must have a license starting at GeoCat Bridge for QGIS v4.1 and above. If you are not interested in support, you can also use the community version of GeoCat Bridge for QGIS.
Note that a Bridge license will also work on GeoCat Bridge for ArcMap and may be used interchangeably.