Does the statement of Sheikh al-Islam Ibn Taymiyyah that the agreed-upon hadiths are authentic beyond doubt mean that there is no agreed-upon hadith whose text has been criticized, and that criticism is only directed at the chain of narration?

We have not found any statements from Shaykh al-Islam Ibn Taymiyyah indicating that what al-Bukhari uniquely narrated in his Sahih takes precedence over what the two Shaykhs (al-Bukhari and Muslim) agreed upon. Rather, Ibn Taymiyyah believes that most of the narrations in the two Sahihs are definitively authentic, either due to their tawatur (being narrated by a large number of people at each stage of the chain) or due to the Ummah's acceptance of them.

What the two Shaykhs agreed upon in their narration is considered to be of the highest degree of authenticity, followed by what al-Bukhari uniquely narrated, and then by what Muslim uniquely narrated.

All the narrations in the two Sahihs are authentic in their chains of transmission and texts, especially those agreed upon. The minor criticisms do not undermine them, as the people of knowledge have unanimously agreed on the truthfulness and authenticity of the narrations in the two Sahihs, and that they have been received with acceptance.