Originally, when WordPress 5.0 came out, the classic editor would be depricated, but Gutenberg is full of bugs, and the demand of existing editors is still large, so it will be still included as a core feature of WordPress.
“Since the Classic Editor plugin is central in this transition, we are considering including it with upgrades to WordPress 5.0,
Support is until 2021
However, it is determined that it will be until 2021, and there will be no support from 2022. It means that it will be “officially supported” until 2021, and will be compatible with all WordPress updates so far.
will be guaranteed to work as expected in the most recent major release of WordPress, and the major release before it.
In fact “Classic Editor” is popular
Currently “Classic Editor” has more than 500,000 installed.
Perhaps because it can not correspond to Gutenberg …