Disabled Gutenberg Block Editor
<?php
// all
add_filter( 'use_block_editor_for_post', '__return_false' );
// Specific post types
add_filter( 'use_block_editor_for_post_type', 'disable_block_editor', 10, 2 );
function disable_block_editor( $use_block_editor, $post_type ) {
if ( $post_type === 'page' ) {
return false;
}
return $use_block_editor;
}