I’m seeing a similar thing on 5.4.1 – I can’t preview or update existing posts or pages. It takes me to the list of posts/pages when I click preview or update and doesn’t save my changes.
It did this some weeks ago, but then seemed to work again for a bit, but now doesn’t work at all. I essentially can’t update the website at all!
I also can’t update my Divi theme, which may be a separate issue, but as the preview and update buttons are actual WordPress buttons I don’t understand how the theme would affect this.
