OneToOne Model delete Cascade in both ways
I think you can use two main options:
1 - Create a signal post_delete on Model B, which will delete the record on Model A: https://docs.djangoproject.com/en/3.2/ref/signals/#django.db.models.signals.post_delete
2 - Override the delete method on Model B: Override django's model delete method for bulk deletion
As it was pointed by @iserranoe in the comments, solution 2 will not work properly when deleting multiple models. Because of that, and to avoid overriding Django default methods, I strongly suggest using post_delete signals