What problem does this address?

I noticed while testing out 6.6 RC3 that, once a post has been published, the Publish button changes to say "Save." On WP 6.5, the button says "Update" when the post is in this state.

In WP 6.6:

In WP 6.5:

I think the word "Save" will be confusing for some users and may lead to confusion over whether a post is actually published, particularly because of its similarity to the "Save Draft" option for draft posts.

Because that button is placed high on the page in a bold color, I expect many users rely on it as an indicator of the post's current status. Seeing "Save" doesn't give a clear indication of whether the post is already live, which may cause them to publish changes that they only intended to save as a draft. In a past life working with a different CMS, we had a similar issue that occasionally caused unfinished copy to be published live on our news website unexpectedly.

My best guess from looking through the records I can find is that this change happened as part of this PR (#60456) while trying to align the post editor UI with the site editor. I think that goal makes sense, but the Save wording may be confusing for users who aren't used to it.

Some of the designs proposed on that PR include other mechanisms to indicate the status of the post more clearly, such as a colorful "Published" badge. I think those would be helpful in reducing the confusion introduced by the word "Save."

What is your proposed solution?

I suggest that we change that button back to "Update" for now, until some of those additional UI elements are available to help provide situational awareness for users.