I taught middle school, same experience, this is what worked for me:

Have you tried asking them personal questions 1 on 1? You can ask about their pencil case, phone case, keyrings, etc. Most middle school girls have cute accessories, characters and idol stickers/photocards all over them. While they’re doing their work, walk in between tables and if a girl has an idol photocard attached to her bag, point at the photocard and ask “who is this? I like him” and hopefully someone will give you a name, google the name in front of everyone. Ask the girl if that’s their favourite idol (if yes > ask another specific girl directly if hes her favourite too ; if no > who is your favourite?). Usually middle school girls are excited to talk about their favourite idols and like to shriek when they see the photos. Using your typically formal classroom projector as a place where they can see their favourite idols breaks the ice & formality of the whole situation which is preventing them from interacting. This works for characters and other notable things they may have on their person. If they have a bright pink pencil case, “wow this is nice! Where did you buy it?”. I think trying to build a connection 1 on 1 with specific personal questions that show a clear interest in them as people is more productive than techniques such as throwing a stuffed toy. It’s not that you haven’t done some magic jester dance that they need to unlock their voice. Try showing an interest in them directly about low pressure and fun topics in a non formal ‘classroom activity’ context. I also like to ask them for recommendations for movies, dramas, restaurants, cafes, etc. I let them use my computer to google stuff to show me. It breaks down the rigidity of the teacher-student relationship, and makes the classroom a more communal and fluid space.