did you want the drop down thats being filtered or the requestor people picker?
ComboBox People picker = Choices([@AD20_1].Requestor)
DropDown being filter by department
If(DataCardValue30.Text ="Information Services" Or DataCardValue30.Text = "Legal" Or DataCardValue30.Text = "Finance" Or DataCardValue30.Text = "Administration" Or DataCardValue30.Text = "Employer Services" Or DataCardValue30.Text = "Member Services" Or DataCardValue30.Text = "Disability" Or DataCardValue30.Text = "Organizational Excellence" Or DataCardValue30.Text = "Communications" Or DataCardValue30.Text = "Investments" Or DataCardValue30.Text = "Office Services" Or DataCardValue30.Text = "Internal Audit",
Filter('Authorizing List', Department = DataCardValue30.Text,
(DataCardValue30.Text ="Human Resources"),
Sort('Authorizing List', 'Full Name'))