How can I disable the scroll-into-view behavior of TScrollBox?

As you wish, here are some suggestions:

• Override SetFocusedControl in the form:

  function TForm1.SetFocusedControl(Control: TWinControl): Boolean;
  begin
    if Control = RichEdit then
      Result := True
    else
      Result := inherited SetFocusedControl(Control);
  end;
  

  Or:

  type
    TCustomMemoAccess = class(TCustomMemo);
  
  function TForm1.SetFocusedControl(Control: TWinControl): Boolean;
  var
    Memo: TCustomMemoAccess;
    Scroller: TScrollingWinControl;
    Pt: TPoint;
  begin
    Result := inherited SetFocusedControl(Control);
    if (Control is TCustomMemo) and (Control.Parent <> nil) and
      (Control.Parent is TScrollingWinControl) then
    begin
      Memo := TCustomMemoAccess(Control);
      Scroller := TScrollingWinControl(Memo.Parent);
      SendMessage(Memo.Handle, EM_POSFROMCHAR, Integer(@Pt), Memo.SelStart);
      Scroller.VertScrollBar.Position := Scroller.VertScrollBar.Position +
        Memo.Top + Pt.Y;
    end;
  end;
  

• Interpose TScrollBox:

  type
    TScrollBox = class(Forms.TScrollBox)
    protected
      procedure AutoScrollInView(AControl: TControl); override;
    end;
  
  procedure TScrollBox.AutoScrollInView(AControl: TControl);
  begin
    if not (AControl is TCustomMemo) then
      inherited AutoScrollInView(AControl);
  end;
  

  Or:

  procedure TScrollBox.AutoScrollInView(AControl: TControl);
  begin
    if (AControl.Top > VertScrollBar.Position + ClientHeight) xor
        (AControl.Top + AControl.Height < VertScrollBar.Position) then
      inherited AutoScrollInView(AControl);
  end;
  

Or use any creative combination of all of the above. How and when you like it to be scrolled only you know.

the simpliest solution would be

var a, b : Integer;
begin
  a := ScrollBox1.VertScrollBar.Position;
  b := ScrollBox1.HorzScrollBar.Position;
  richEdit1.SetFocus;
  ScrollBox1.VertScrollBar.Position:=a ;
  ScrollBox1.HorzScrollBar.Position:=b ;
end;