If your instance defederates another one then your instance will not download posts or comments from members of that instance. You won’t be able to join communities from that instance either. So afaik that is the most effective way to prevent seeing any content from or interacting in any way with members of transphobic instances. But I’m sure someone more knowledgeable than me will chime in.

If you see any transphobia on this community please report it and it will be removed and the commenter banned permanently.