java.io.FileNotFoundException: /storage/emulated/0/New file.txt: open failed: EACCES (Permission denied)

If you are running in Android 29 then you have to use scoped storage or for now, you can bypass this issue by using:

android:requestLegacyExternalStorage="true"

in manifest in the application tag.

I suspect you are running Android 6.0 Marshmallow (API 23) or later. If this is the case, you must implement runtime permissions before you try to read/write external storage.

Implement runtime permission for running your app on Android 6.0 Marshmallow (API 23) or later.

or you can manually enable the storage permission-

goto settings>apps> "your_app_name" >click on it >then click permissions> then enable the storage. Thats it.

But i suggest go the for first one which is, Implement runtime permissions in your code.