You will have to file a CA return and pay CA tax on the money you earned working in CA.
If you still consider yourself a MI resident (i.e. you plan to return to MI in the foreseeable future), you will file a resident MI tax return and a non-resident CA tax return. MI will tax all of the income you earned in CA (plus any other income you may have had in 2020), but they will give you a credit (against MI tax) for the tax you paid to CA on the income earned there.
Complete the Personal Interview questions carefully, making sure that you choose that you were a resident of MI for the entire year but did "Earn Money in another state."
Also, you will need to complete the CA state tax interview in TurboTax before completing the MI state tax interview. This way, the program will have calculated your CA tax and know how much of a credit you will get toward MI tax.
