Simple apps may want to migrate, a simple router doesn’t ‘need’ the whole router folder and multiple routes but the toolchain seems to be hard coded (I’ll keep the opinions to myself). However, as a workaround, create/keep the /router folder with index.js/ts inside and inside that file…

import router from ‘…/router.js’ // or whereever you want to put it…
export default router;

Done, hard coded path averted.