What is the authenticity of the hadiths concerning Maria al-Qibtiyya? Did the Messenger love her only for her beauty? Did the Messenger dislike Sawda? Is describing Sawda as not beautiful considered backbiting? And is affection related to outward appearance and beauty?

Both narrations are not authentically attributed. As for the first: it contains Al-Waqidi, who is abandoned (matruk), and his شيخ (teacher) has no biography found for him, while there was another narration about Maria (may Allah be pleased with her) indicating her good character.

As for the second: it contains Muhammad ibn al-Hasan ibn Zabalah, who is a liar whose hadith is abandoned (matruk), and Muhammad ibn Musa al-Fitri, who is truthful but accused of Shi'ism, and Fulayh ibn Sulayman, who is truthful but makes many errors. Additionally, this narration contradicts what has been continuously transmitted (mutawatir) about the Prophet (peace be upon him) regarding his justice among his wives, and that if the Prophet (peace be upon him) had been pleased with her, he would have married her, as he did with Juwayriyah and Safiyyah.

As for Sawdah bint Zam'ah (may Allah be pleased with her): there is no narration indicating that the Prophet (peace be upon him) disliked her or divorced her. Rather, she gifted her day to Aisha (may Allah be pleased with her) seeking the pleasure of the Prophet (peace be upon him). It is not authentically reported that she was not beautiful; rather, she was tall. Moreover, backbiting the deceased is generally like backbiting the living, but even more severe.