You're halfway there already. Create a copy of your "Date Aggregator" parameter - call it "Date Aggregator Line" or something similar. Then create a duplicate of your Date Selector field and change it to use the 2nd parameter:
DATE(DATETRUNC([Date Aggregator Line], [Date]))
Then, on your bar chart, replace the Date Selector field on columns with the new calculated field you created with the second parameter.
On your dashboard, show the second parameter. Now the first will control the line chart and the second parameter will control the bar chart.
Thank you so much!
Welcome! Happy to help!