Are the hadiths mentioned in Sahih Muslim authentic, especially those that contradict the sayings of some scholars or those that are said to be from other than the Prophet's words? And has the Ummah unanimously agreed upon the authenticity of Muslim's hadiths?

Everything that Imam Muslim authenticated in his Sahih is authentic, and the Ummah has accepted it with approval, except for a very small portion. Ibn al-Salah held that whatever Muslim and al-Bukhari authenticated in their books is definitively authentic, and one attains theoretical knowledge of its authenticity in reality, due to the Ummah's acceptance of it, except for those whose dissent is not given weight. However, what has been criticized in these two books and impugned by reliable memorizers (of Hadith) is an exception, due to the lack of consensus on its acceptance. This is rare. Al-Albani stated that scholars have accepted the two Sahihs with approval, and they are free from weak and denounced hadiths. As for the two hadiths mentioned in the question, al-Albani did not weaken them; rather, he authenticated them, even though the hadith "Allah created the dust on Saturday" is among the hadiths that have been criticized regarding Muslim, and scholars have differed concerning its authenticity. As for the hadith of "the five sucklings," Sheikh Ibn Uthaymeen did not weaken it, nor is it among the hadiths that al-Daraqutni criticized Muslim for.