نوشته شد / نوشته می‌شود

Change the roles. In نویسنده نامه را نوشت, نامه را is the object. In نامه نوشته شد, نامه is the subject and loses that object marker. The event still involves writing, but the writer need not be named.

Build from a transitive verb. نوشته is the participle of نوشتن. نوشته شد places the passive event in the past; نوشته می‌شود can describe current or habitual writing. The participle keeps the lexical action while شدن supplies the finite form.

Place negation on the auxiliary. نامه نوشته نشد negates the passive writing event. این گزارش هنوز منتشر نشده است has the compound publishing construction and a negative perfect auxiliary. Retain the full compound instead of treating منتشر as an unrelated adjective.

Compare a change in state. سارا خسته شد says Sara became tired. It does not by itself describe an unnamed person tiring her. A real passive relates an active transitive action to its affected participant; the presence of شدن alone is not the test.