Today has taken the date of modification of that post, great !!
But it turns out I’ve changed the permalinks including the category on url. I do not know if that is why he has taken it back. I think that if I had not changed the permalinks url, Google could still show be the same date of creation.
On the other hand what I would like you to do in GeneratePress is that once a post is modified, only the modification date appears. I think the issue of having two dates together is very rare for the public and for Google.