I don't think that you can use the security filters dynamically as you want.
for that, I have a suggestion for customization as follows:
Step 1.) There is a Field on User Setup >> Salespers./Purch. Code: Fill in the Purchaser Code user-wise.
Step 2.) Add a Filter of "Salesperson./Purch. Code" in Purchase Order List Page on Open Page Trigger as follow
trigger OnOpenPage()
var
UserSetup: Record "User Setup";
begin
UserSetup.Get(UserId);
FilterGroup(0);
SetRange("Salespers./Purch. Code", UserSetup."Salespers./Purch. Code");
FilterGroup(1);
end;
Note: Please mark my answer as varified if this was helpful.
