In reply to Anne McCarthy.

Nice! Thanks for breaking all this down and sending it to the right places.

You mentioned that the settings didn’t stick when you’re using the Top Toolbar but I wasn’t able to replicate that when just using WordPress 5.6.2 without any additional plugins installed. I was able to turn that preference on, publish a post, navigate to wp-admin, and start a new post with the preference saved.

This works for me on the post/page screens. It doesn't in the site editor.