Look, every stutter speak/sing fluently when they alone. It’s the anticipation of knowing that you will stutter that makes one stutter the more. My mom used to be a stutter she overcame her while I was a kid. My sisters too stuttered, they overcame their by age 25. I still have a stutter but mine isn’t noticeable unless you’ve known me for a long time, I do speak fluently most of the time, use to have a bad stutter. I was good at disguising my stutter growing up. One way that helped me kinda become fluent is by prolonging my words like I’m singing it and also using a lot of hand gestures.