Ever since WordPress unveiled the drag-and-drop “Gutenberg” editor a few years ago, which I use on here (and my first post with it was three years ago today), there has been talk of when it might be extended to help edit your entire site. That time is coming very soon.
As of today, you can use the Gutenberg editor in your post. All of this content I’m writing is using Gutenberg, but I can’t use it to edit the navigation menu, sidebar items, or the footer.
While it won’t be a full site-wide editing tool immediately, the first pieces of it should come along with WordPress 5.8 this July.
If you want to learn more, this summary from Justin Tadlock is excellent and should answer many of your questions. The next few releases of WordPress will really be some major milestones, so they’re good ones to keep a close eye on.