Both are acceptable in modern English. Whom is increasingly viewed as archaic. Collins online dictionary https://www.collinsdictionary.com/dictionary/english/whom PRONOUN the objective form of who, used when who is not the subject of its own clause whom did you say you had seen? he can't remember whom he saw ▶ USAGE It was formerly considered correct to use whom whenever the objective form of who was required. This is no longer thought to be necessary and the objective form who is now commonly used, even in formal writing: there were several people there who he had met before. Who cannot be used directly after a preposition – the preposition is usually displaced, as in the man (who) he sold his car to. In formal writing whom is preferred in sentences like these: the man to whom he sold his car. There are some types of sentence in which who cannot be used: the refugees, many of whom were old and ill, were allowed across the border

"Who is ignoring whom?" is correct. She is ignoring him. Use "who" when the answer is "he" or "she" or "they" Use "whom" when the answer is "him" or "her" or "them" To whom should I give this cake? Give it to him. Who is the manager of this store? She is. Please give this to whomever you wish. Ok. I will give it to them. I am going to find whoever is responsible for this. They are responsible for this. Many native speakers don't even know the difference, though, and whom is pretty uncommon. In my first example, you would almost certainly hear someone say "Who should I give this cake to?" (another reason this sentence is not grammatically correct is the fact that it ends with the word "to" which is a preposition, and you are not supposed to end a sentence with a preposition. However, both of these grammar rules are largely ignored in everyday conversation and even in somewhat-formal written communication)