Hi @CK
Welcome to Microsoft Q&A! Thanks for posting the question.
As per the error message expression body('Get_item')['Title'] means that the output of Get_item action doesnot have the property 'Title'.
This happens only in the scenario when you have created the item without the Title on your selected list on SharePoint site.
The same can be verified by navigation to the run history of your logic app and verify if the output has a missing Title field for your "Get item" action or navigate to your SharePoint site list item and verify if there is any item with missing Title.
If in your business requirement this can be an empty field then you can add one more action to verify if the Title property exists in the output before executing the "Update Item" action.
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