discourse/app/assets/javascripts/admin/addon/controllers/admin-config-flags-settings.js

import Controller from "@ember/controller";
import { action } from "@ember/object";

export default class AdminConfigFlagsSettingsController extends Controller {
  filter = "";
  queryParams = ["filter"];

  @action
  filterChangedCallback(filterData) {
    this.set("filter", filterData.filter);
  }
}