Is a person considered a polytheist if they are overcome by waswas (whispers/temptations) during prayer and dhikr (remembrance of God), causing their intention to turn towards other than Allah?

These are whisperings from Satan to divert you from obeying Allah. Therefore, you must disregard them and pay them no mind, and continue with your worship. These thoughts do not harm you as long as you dislike them, and Allah has forgiven this Ummah for what they whisper to themselves, as long as they do not act upon it or speak of it. Seek refuge with Allah from Satan and proceed with your worship.