Is the consensus of all scholars a must condition for ijma?

It's clearly proved from hadith of bukhari that not all companions have Ijma to caliphate of Abu bakr when he delivered the sermon after becoming caliph. https://sunnah.com/bukhari:4240 Imam Shafaee said all scholars need to agree for ijma. Sk. Utheymeen has similar view. > Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: In linguistic terms, ijmaa‘ means resolve and agreement. In shar‘i terms, it means the agreement of the mujtahids of this ummah after the death of the Prophet (blessings and peace of Allah be upon him) on a shar‘i ruling. By saying “agreement” we exclude differences of opinion; if there is a difference of opinion, even from one person, then we cannot say that there is ijmaa‘. Source : https://islamqa.info/amp/en/answers/201682 I see contradiction between election of Abu bakr and view of later scholars including imam ash shafaee. Hence the question is the consensus of all scholars a must condition for ijma