Is it Sunnah to repeat the Mu'awwidhat (Surahs Al-Falaq and An-Nas) three times and recite Al-Fatihah and the beginning and end of Surat Al-Baqarah with the intention of starting a new recitation (khatmah) when completing the Qur'an in a group?

It has not been reported in the Sunnah that the Mu'awwidhat (Surahs Al-Falaq and An-Nas) are to be specifically repeated when concluding the Qur'an, and it is better not to do so, because some scholars have considered specifying certain surahs for repetition to be among the innovations (bid'ah). As for connecting one ختمة (completion of the Qur'an) with another by reciting Surah Al-Fatihah and the beginning of Surah Al-Baqarah, this is sunnah according to the consensus of scholars.