This is a pretty good explanation of the new editor for WordPress. This theme from my current site is based on using the old editor and has not been upgraded and I doubt it will be. Picked it up right before Gutenberg was released and had put too much work into it to drop it. So, I will use it for a couple of years and replace it when I have to. You can update to the newest version of WordPress without problems, you just need to install a classic editor plugin and it works great. I’ve done this on a couple of my sites without a hitch. I am getting ready to actually utilize the new Gutenberg style editor on my wife’s website, I will post a response here when I get it done and let you know how it went.