Steps to reproduce the behavior

1. On a Simple site, create a new post
2. Click on the Permalink section on the post settings
3. Try to edit the post's slug

What I expected to happen

To see the URL Slug field to be able to change it.

What actually happened

There's no URL Slug field. It only shows the field once you save the post as a draft. This isn't happening when creating pages.

Context

Browser / OS version

Chrome 88.0.4324.192
Mac OS X 10.15.7

Does this happen on simple or atomic sites or both?

It only happens on Simple sites, wasn't able to replicate on Atomic and WordPress.org sites.

Reproducibility

Consistent.

Screenshot

When creating the post, before saving:

After saving the draft:

Reported by the user on 3768342-zd-woothemes