Hey Niccolo,

I am sorry that delay of this reply,

when I hit "preview" in the post composer I get redirected to a page with a 404 error.
I have version 5.0.22

I tried in your frontend blog preview, it seems work fine.
If you preview the post from backend, you have to login in your frontend first, if not guest user do not have permission to preview section.
And make sure your browser allow to pop up. Check my screenshot below.

Besides this, I am not sure to understand how to set as "unpublished " a post when creating it. If I save it it gets published automatically, which also triggers the facebook autoposting... not good for posts I need to update later.

It seems like that unpublished is not shown up now.

However, I've temporary added for you and set environment mode to `development` , you should see the `unpublished` button from the composer now, check my screenshot below.

*Note: if you would like to update your `unpublished` post and don't publish first, you have to click back `unpublish button` again instead of `update button`.

By the way, I will consult this issue when the week start.