Borrowed from a community note on Dead🐦:

The #DOJ is not the personal law firm of the President. "The Attorney General represents the United States in legal matters generally and gives advice and opinions to the President and to the heads of the executive departments of the Government when so requested." https://www.justice.gov/ag#:~:text=The%20Attorney%20General%20represents%20the,person%20before%20the%20Supreme%20Court.