Many people don’t like the newly added WordPress Editor (Gutenberg) in the recent versions of WordPress by default.
If you’re one of the people that likes the classic editor better,
you can get it back by adding only one line of code to the end of your functions.php file.
Simply add the following code right before the last PHP closing tag.
add_filter( 'use_block_editor_for_post', '__return_false' );