Sovereignty transfer doesn’t mean displacement. If European settlers want national self-determination, they can go back to their nation-states, or they can live under the sovereignty of another nation. Social justice requires that the colonizers cede back the power over the land that they took through centuries of genocidal violence.
Edit: also good to note, restorative justice would be for all the European settlers to return the land to a healthy state under the dominance of the indigenous peoples of the land. Retributive justice would be for the indigenous peoples to invade and violently occupy Europe for 600 years. No one is even asking for restorative justice at this point, just an end to the genocide and occupation.