Index: src/js/media/views/attachment.js
===================================================================
--- src/js/media/views/attachment.js	(revision 58163)
+++ src/js/media/views/attachment.js	(working copy)
@@ -199,6 +199,11 @@
 			method = 'toggle';
 		}
 
+		// Avoid toggles when the command or control key is pressed with the enter key to prevent deselecting the last selected attachment.
+		if ( ( event.metaKey || event.ctrlKey ) && ( 13 === event.keyCode || 10 === event.keyCode ) ) {
+			return;
+		}
+
 		this.toggleSelection({
 			method: method
 		});
Index: src/js/media/views/modal.js
===================================================================
--- src/js/media/views/modal.js	(revision 58163)
+++ src/js/media/views/modal.js	(working copy)
@@ -181,6 +181,29 @@
 	},
 
 	/**
+	 * Handles the selection of attachments when the command or control key is pressed with the enter key.
+	 *
+	 * @since 6.6
+	 *
+	 * @param {Object} event The keydown event object.
+	 */
+	selectHandler: function( event ) {
+		var selection = this.controller.state().get( 'selection' );
+
+		if ( ! selection.length > 0 ) {
+			return;
+		}
+
+		if ( 'insert' === this.controller.options.state ) {
+			this.controller.trigger( 'insert', selection );
+		} else {
+			this.controller.trigger( 'select', selection );
+			event.preventDefault();
+			this.escape();
+		}
+	},
+
+	/**
 	 * @param {Array|Object} content Views to register to '.media-modal-content'
 	 * @return {wp.media.view.Modal} Returns itself to allow chaining.
 	 */
@@ -214,6 +237,13 @@
 			this.escape();
 			event.stopImmediatePropagation();
 		}
+
+		// Select the attachment when command or control and enter are pressed.
+		if ( ( 13 === event.which || 10 === event.which ) && ( event.metaKey || event.ctrlKey ) ) {
+			this.selectHandler( event );
+			event.stopImmediatePropagation();
+		}
+
 	}
 });