Some say that Jihad is the sixth pillar of Islam. Is this a basis for takfeer declaring one’s expulsion from Islam?

No, many scholars of Islam held the view that Jihad is a sixth pillar of Islam due to many hadiths and verses that state about greatness, importance and virtues of Jihad. It is a valid difference of opinion between scholars, and that is permissible in Islam. Therefore, it is not a basis for takfeer.