From the screenshot of your csv file I can see that your variable is called date not Date (R is case sensitive), also, the dates are already in the ISO standard format Y-m-d (the only one R uses for dates) so you shouldn't try to parse it with a different format (i. e. "%m/%d/%Y").
If you need more specific help, please provide a proper REPRoducible EXample (reprex) illustrating your issue.