There are a few “standard” Fields (i.e., not Custom Fields) which we don’t use (e.g., Due date, Projects). In my Project’s Customize → Fields section, they are toggled off, yet they still appear when viewing a Task Detail Pane. Do I need to delete these Fields to get them to go away? What is the purpose of a Customize → Fields toggle?
I’m afraid it’s not possible to hide those several built-in standard fields. Customize lets you manage columns in List view and manage your custom fields.
I’ve moved this post to #forum-en:product-feedback so that now you and others can add your vote for this request at the top of the thread.