To make adjustments for the Michigan portion of your income, when you start your Michigan return and your state that you were a part-year resident and then you will be asked the dates you resided in Michigan. It would be from 1/1/2021 through the date you moved out of state. When you get to the screen that says Your 2021 Michigan taxes are ready for us to check and there is a list of the sections of the return. Click on Income and there will be a screen for each area of income on your Federal return where you designate the amount that goes to Michigan residency. When you get to the question about Capital Gains and Losses enter the amount attributable to Michigan. You will have to total of the sales from your 1099-B the amount that is attributable to the period that you were a resident of Michigan.
Entering the amounts through the procedure above should avoid you have to make any adjustments. In Michigan you would only enter totals you would not enter individual transactions.
The instructions for Michigan 1040 Schedule 1 - Adjustments to Capital Gains and Losses is on Line 3 of Schedule 1. According to the below instructions, this would only be used for three reasons and your situation would not be one of those reasons.
Line 3: Use Michigan Adjustments of Capital Gains and Losses (MI-1040D) and related Michigan Sales and Other Dispositions of Capital Assets (MI-8949) only if you have capital gains or losses attributable to: (1) an election to use Section 271 treatment for property acquired before October 1, 1967; (2) the sale or exchange of U.S. obligations which cannot be taxed by Michigan; or (3) the sale or exchange of property located in other states. If you reported gains on U.S. Form 4797 on property acquired before October 1, 1967, or located in other states, adjust the gain on the Michigan Adjustments of Gains and Losses From Sales of Business Property (MI‑4797). Enter gains from the Michigan column of MI-1040D, line 12, and MI-4797, line 18b(2). Instructions are with each form.
This article from Michigan.gov When Adjustment on Michigan Capital/Gain Loss is Necessary explains when you need to adjust.
However, if you enter the capital gains/losses as stated above through the designation process of the state return, you would not need to make an adjustment.
