These are two separate terms which seem to have been intermingled in the Question:
1) Ijma and Tawatur (as established history)
2) Mutawatir Hadith (as category of Ahaad)
Following thread explains the difference between these terms:
Discussion 87226
The Book shared above committed the same mistake of mixing these two terms. What they did was they took some Mutawatir Hadith narrations and made a false claim of historical tawatur for them since its origination from Prophet Muhammad (sws). In terms of historical transmission of words, it is only Quran which has achieved perpetual concurrence (qoli tawatur) in addition to Ijma to the highest level where in simple terms, its each and every word is part of established history now (Tawatur).
As far as the last Hajj of Prophet Muhammad (sws) is concerned (i.e. Hajjat-ul-Wida), the fact that Prophet Muhammad (sws) attended that last Hajj and gave a final sermon is something which falls under Ijma and this information is transmitted through Tawatur (also known as established history). The details pertaining to that last sermon however are a domain of Akhbar-i-Ahad. Another fact which needs to be kept in mind is that as per the reports, it appears that the Prophet (sws) delivered three different sermons: One in Arafa (9th Zulhajja), Second one on Youm-e-Nahr (10th Zulhajja) and a Third one in between Ayam-e-Tashreeq (most probably 11th Zulhajja). Some people say that one more sermon was delivered on 7th Zulhajja as well (thus making the total number of sermons as four). The total narrations reported in different books regarding this last sermon (all three occasions) roughly turn out to be 1163 (including same chains repeated in different books) and are primarily narrated from the following Sahaba who have narrated the relevant parts according to their own preference or maybe it got truncated by one of the narrators in the process of transmission (some narrating only a small portion of it while a few narrating a bigger portion):
1) Jabir bin Abdullah (rta) (https://sunnah.com/muslim:1218a)
2) Nafi Bin Haris (rta) (Also known with name Nafi Bin Masruh) (https://sunnah.com/bukhari:67)
3) Nubait bin Shareet (rta) (https://islamicurdubooks.com/hadith/hadith-.php?tarqeem=1&bookid=24&hadith_number=18722)
4) Umm-e-Abi Harrah Ar-Raqqashi (rta) (https://islamicurdubooks.com/hadith/hadith-.php?tarqeem=1&bookid=24&hadith_number=20695)
5) Abdullah Ibn-e-Umar (rta) (https://sunnah.com/bukhari:6043)
6) Amru Bin Al-Haus Al-Jashmi (rta) (https://sunnah.com/ibnmajah:3055)
7) Abu Saeed Al-Khudri (rta) (https://sunnah.com/ibnmajah:3931)
8) Al-Adaa bin Khalid Al-Qaisi (rta)
9) Saraa Bint-e-Nabhan (rta)
10) Abdullah Ibn-e-Masud (rta) (https://sunnah.com/ibnmajah:3057)
11) Wabisa bin Moeed Al-Asadi (rta)
12) Ammar bin Yasir (rta)
13) Abdullah bin Zubair (rta)
14) Al-Haris bin Amr Al-Sahbi (rta) (https://islamicurdubooks.com/hadith/hadith-.php?tarqeem=1&bookid=24&hadith_number=15972)
15) Fazala bin Ubaid Al-Ansari
16) Abdullah Ibn-e-Abbas (rta) (https://sunnah.com/bukhari:1739)
17) Hizaim bin Amr Al-Saadi (rta)(https://islamicurdubooks.com/hadith/hadith-.php?hadith_number=18966&bookid=24&tarqeem=1)
18) Hujair bin Abi Hujair Al-Halali (rta)