Once a story has been published, it is too late for criticism to improve that story. That's what a beta-read is for.
Criticism or praise of the story may, of course, enable the writer to become a better writer, long term. In that context, I find writers who say they want "constructive criticism" but object to "harsh criticism" generally mean they still confuse criticism of their story or their writing with a personal attack, and it's better to avoid beta-reading for those writers.
Once a story is published, it is fair game for anyone to write about however they please - a writer who can't take being criticised harshly had better not publish.
no subject
Criticism or praise of the story may, of course, enable the writer to become a better writer, long term. In that context, I find writers who say they want "constructive criticism" but object to "harsh criticism" generally mean they still confuse criticism of their story or their writing with a personal attack, and it's better to avoid beta-reading for those writers.
Once a story is published, it is fair game for anyone to write about however they please - a writer who can't take being criticised harshly had better not publish.