If you lived and worked in CA for all of 2020 then you file a CA tax return. Your drivers license does not determine where you file your tax return. Living and working in CA means you had CA sourced income that is taxable in CA. If you did not live or work in MI at all in 2020 then the CA state return is the only state return you need to prepare and file.
Not being sure if you are staying in CA is not a factor in how you file for 2020. For 2020 you say you were in CA. If you leave CA sometime in 2021, that will affect your tax return for 2021 when you file in 2022.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
