See related meta post I answered: https://meta.stackoverflow.com/questions/369410/why-is-there-no-explanation-hint-when-a-big-ui-change-occurs What is this type of functionality called (aside from Tutorial).
From my post:
I will say this..the one thing Google and some of the other major sites do that probably stackexchange could / should do is...
When a new layout or major update is done google makes the site's background kind of grayish and sets focus to new elements with an arrow pointing at something new and explaining how it works. You click "next" and it shows you the next feature, etc. You can always click the "I got it" button to tell google, "hey I get what you mean now get out of my way and let me use it" (they do this in the new gmail client as well).
It is pretty effective because it becomes a sort of tutorial for the end user. It signals to the user that something has changed (by graying out the background). It highlights the new features by bringing focus (color, arrows, text, etc.) to it. It explains what it does and actually lets you interact with it. It is progressive in that it goes out of its way to show you the next tid bit of new feature(s) within the update. It's dismiss-able for power users who can pick up new features and understand them right out of the box.
Sample library that uses this type of technique: https://introjs.com/