My speech therapist said that music and singing is dealt with by a different "area" of the brain, and because singing relaxes people, the stutter eases or stops during the singing.  I used to perform in musical theatre etc, but can't now due to mobility issues and my Tourette's tics are an "insurance hazard". I developed a bad stutter in 2022, plus I was diagnosed with adult onset Tourette's with vocal tics and Functional Neurological Disorder in 2023.  We don't know if the stutter and Tourette's are a result of my 2020 spinal injuries, or if something happened during an emergency spinal op in 2021 (first hospital refused to operate in 2020, and I ended up in emergency surgery just before Christmas 21.  One wrong turn of the head and I would have been a paraplegic.) The other possibility is the antidepressants I was prescribed because of the pain and lack of mobility etc., may have interacted with my medications I need to take for my autoimmune conditions.  We stopped the antidepressants, but by that point, the stutter and as yet undiagnosed Tourette's had "set in" so to speak.