Since the introduction of WordPress 5.x, Gutenberg had been added as the default editor. To me personally, i think it was a mistake to do so.
Don't get me wrong, i like Gutenberg - it's a powerful editor that allows anyone to quickly knock up a visual page. However, the issue i have is that not everyone wants to use it and it can break some of the existing off-the-shelf themes.
I get why it was developed but majority of my clients just don't care. All they are interested in is to update their site content, not build a visual page. The other reason is, some times you don't want to leave that power to your clients to be able to mess around with the layout of the site, unless they have an in-house designer.
So this new editor (Gutenburg) I believe was solely aimed at those that build their own website for their own business, which is great. But why not make it a plugin that a WP admin can activate if they chose to use it instead forcing everyone to use it as the default editor.
Luckily, it is real easy to get back the old classic editor. It is available as a plugin called 'Classic Editor'. Looking at the installed stats for Classic Editor, it is hugely popular and it seems there is a large portion of folks like myself that want replace Gutenberg.
There are a few ways of getting the old editor back. The easiest and recommended way is to go to your Add plugins page and install 'Classic Editor', see below on how to accomplish this: