Culturally responsive teaching is not a substitute for social justice and anti bias teaching
Montessori sometimes has a reputation as being multi-cultural or that it teaches lots about the world. The Montessori curriculum is indeed rich in curriculum experiences that can be used as windows into the world. While these certainly help increase a child's knowledge of the world we can use the Montessori curriculum to help us further develop our practice using modern pedagogical ideas.
Montessori always wanted her classrooms to be culturally responsive. For example the practical life activities in a 3-6 class are meant to help a child practice skills they will come across in their everyday life. This links to the idea of culturally responsive teaching or CRT. CRT is about making learning relevant and effective for learners already at a school by affirming students' cultural knowledge, life experience and so on.
Social justice builds upon some ideas of CRT and seeks to explicitly affirm through the whole curriculum diversity, justice and activism.
As an example, a school may have a group of children from the south of Somalia and may have a practical life activity that affirms these children. This is not the same as helping the above group of children advocate when they or others in their community face prejudice for housing because of their race.