You want to remove the style from single post. And the “single post” term is confusing.
Whether you need it for a single post or the single post template.
In either case you have to use your code with conditional and your code may look like this.
If you want to remove from all posts(not pages but including custom post types).
add_filter( 'the_content', function( $content ){
if(is_single()){
return str_replace( ' style="', ' data-style="', $content);
}
else{
return $content;
}
});
If you want to remove from all posts(only WordPress post, not custom post type or pages).
add_filter( 'the_content', function( $content ){
if (is_singular('post')) {
return str_replace( ' style="', ' data-style="', $content);
}
else{
return $content;
}
});
is_singular is the WordPress API conditional to check post types.
https://developer.wordpress.org/reference/functions/is_singular/
If you want to remove from only one particular post.
add_filter( 'the_content', function( $content ){
if(is_single([POST-ID])){
return str_replace( ' style="', ' data-style="', $content);
}
else{
return $content;
}
});