it "should" be enough to add the "Access-Control-Allow-Origin: *" to the response or server but I don't know what your using under the hood.
either way though I managed to make it works. turns out it was only throwing the CORS errors for http requests and it could connect over websockets fine.
Its here https://next.nostrudel.ninja/#/relays/cache if you want to test it. should be able to enable it then the app will start using ti to cache everything