What I found out so far (I will keep editing the comment with updates):

There are two different errors, introduced with different nightly versions:

4.0.0-29139240.726ac60e -> last versions which works
4.0.0-29144650.ca2dff25 (this PR) -> problem introduced (nuxt.options.experimental.extraPageMetaExtractionKeys is not iterable)
... other versions
4.0.0-29159380.0f7d8778 (this PR) -> problem introduced Cannot find module as a very long path is added to .output/server/index.mjs.
- this path in server/index.mjs leads to the error: import '/Users/[...long-file-path...]/nuxt-app/node_modules/.pnpm/@sentry+nuxt@9.30.0_magicast@0.3.5_nuxt-nightly@4.0.0-29187291.758a1773_@parcel+watcher_0d3c1dd05a9518487524189fb0109748/node_modules/@sentry/nuxt/build/module/runtime/plugins/sentry.server';
- instead of (where it still worked): import './chunks/virtual/_sentry-release-injection-file.mjs';

Fixes

nuxt.options.experimental.extraPageMetaExtractionKeys is not iterable: fix(nuxt): safe-guard extraPageMetaExtractionKeys nuxt/nuxt#32510

nuxt-4 (canary) Test Failed #16762