I work in a field that's heavily dependent on good references (i.e. not tech). In other words, when I apply to a new job, I have to give the name and contact information of a reference, and the prospective new employer will contact that person and expect them to say positive things about me and not simply confirm my job titles and dates of employment.
I need to leave my current job because my manager is abusive and toxic. I think he thinks that he's giving me constructive feedback, but it's always in the form of berating and belittling me for small mistakes or even things that are unrelated to my job duties, such as not being excited enough about something that he's showing me. He micromanages me at times, but also tells me I need to be more independent, but then when I want to discuss his suggestions about how to do my job, he becomes upset about me questioning his authority. Many other people in my organization also believe that my manager is very difficult to work with.
My current contract is up soon and I'm not planning on renewing it, because I believe that continuing to be in this toxic environment is bad for my mental health and that prolonged exposure will negatively affect my confidence that I will bring to future jobs. However, I also am not sure whether I will find a new job right away because of the economic recession caused by the COVID-19 pandemic.
I need to be able to use my current manager as a reference. I believe that despite the way that he treats me, he also recognizes that it would be difficult to find someone else to do my job as well as I do it, and besides, I don't have anyone else who can serve as a reference.
When I quit my job, I need to avoid burning bridges. But my manager will almost certainly ask me why I'm quitting, and it's unlikely that I'll already have a new job lined up to be able to tell him that I'm switching to a new job. He will be curious to know why I am quitting without knowing what I'm doing next. How do I approach this situation so that I can give him a satisfactory (possibly untruthful) answer so that I can still use him as a reference when an appropriate opportunity arises?