Copy Whats new Text from a previous release

Huh? Aside from it being a field called "What's New in This Version", and putting old text in doesn't make much sense, why don't you just go into App Store Connect for the previous release, and copy the text from there?

Alternatively, keep a copy of the text you use for each release, and store it in an archive along with the source code and assets etc. for that release. That way, you can always go back to any version of your app and see exactly what you wrote and what code and assets you had.

I do this, and base my next version off the previous version by simply copying the archive and increasing the version numbers.

If you think Apple should implement this in App Store Connect, you can raise a suggestion at: https://feedbackassistant.apple.com/

Raised a suggestion: FB17496514

If you want to copy so that users may see recent modifications, that's probably useless. In fact, user can see the complete history of 'what's new' in all versions, just by tapping on the what's new label.

Isn't it enough ? And that would avoid duplicate text in the history.

I used a third-party tool called Fastlane - it allows you to upload release notes with a single command. You can keep your "What's New" texts in plain .txt files and push all translations at once with just one command.

lane :update_release_notes do
  deliver(
    metadata_path: "./fastlane/metadata",  # points to your local metadata
    skip_binary_upload: true,              # don’t upload any .ipa/pkg
    skip_screenshots:    true,             # don’t upload screenshots
    skip_app_version_update: true,         # (optional) leave version untouched
    force:                true             # skip the HTML report step
  )
end