It occurs to me, I may not have said how to do that.

You have to go to a post and click the edit button then

1. Click on the button (with 3 dots ) on the top right of the post you are editing.
2. Scroll down to the very bottom and you will find an option which says “Switch to Classic Editor”. Click that and you are done.

It carries over to new posts, thank goodness.

From Here: https://wordpress.com/forums/topic/revert-back-to-classic-editor/