I see that you are trying to update a record. In the earlier steps of your flow, did you try to "Get a record" or "List records"? If no, then you will not be able to get the field values in the dynamic content picker. The update record action in your flow right now updates only one record and you have to put a unique identifier (e.g., record key id) for this step.
If you are using the action "get a list of records" and updating multiple actions, then you can create an apply to each loop and select the list of record there, create a new action -> update record and then select the record identifier to update multiple records.
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