Ghost/ghost/admin/app/routes/designsandbox.js

import Route from '@ember/routing/route';
import {inject as service} from '@ember/service';

export default class DesignsandboxRoute extends Route {
    @service config;

    beforeModel() {
        super.beforeModel(...arguments);
        if (!this.config.get('enableDeveloperExperiments')) {
            return this.transitionTo('home');
        }
    }
}