We completely gutted large parts of JFBConnect to be compatible with Joomla 4. This looked like it slipped through the cracks on testing.
In /components/com_jfbconnect/views/account/tmpl/default.php, can you add the following statement around line 16 after the other use statements:
use Joomla\CMS\Router\Route;
The change will be checked in for the next release.
-Melissa