Many ADHD partners carry a great deal of shame from childhood and the critiques that they got in childhood. Try to drop into a structured conversation like the learning conversations where it slows down the conversation, take some of the emotion out of it. Sometimes the shutdown is just straight up overwhelm, in which case, using that verbal cue can be very useful.
Many romantic relationships touched by ADHD are marked by misunderstandings and emotional outbursts. Effective communication skills, however, can be learned. Melissa Orlov teaches strategies that will resolve conflict with your partner.