https://docs.sentry.io/platforms/javascript/guides/nextjs/configuration/tree-shaking/ has no information regarding exporting the captureRouterTransitionStart in case of tree-shaking

Also file is called main.js not instrumentation-client.ts (js) - why?

Should it be like this? Not clear

import { captureRouterTransitionStart } from "@sentry/nextjs";
// ...
export const onRouterTransitionStart = captureRouterTransitionStart;