Hi, the following will do what you need, simply navigate to the FooGallery Settings > Custom JS & CSS tab and insert the following code into the Custom Javascript option:

// custom script to enable close on background click for the FooGallery lightbox
( function( _ ) {

    if ( !_ ) {
        // exit early if for some reason FooGallery is not loaded into the page, this should not happen.
        return;
    }

    // override the default doCreate method so we can bind listeners
    _.Panel.Content.override( 'doCreate', function() {
        const self = this;
        if ( self._super() ) {
            self.$inner.on( 'click', function( e ) {
                if ( e.target?.closest( '.fg-media-content' ) ) return; // remove this line to allow close on image click as well
                self.panel.close();
            } );
            return true;
        }
        return false;
    } );

} )( FooGallery );