Changing the font size of a row - view-base tableview

So I'm following this code here where I'm using a tableview to display the files contained in a folder along with a group cell to display the name of the current folder:

Here's my tableView:isGroupRow method: method which basically turns every row with the folder name into a group row (which is displayed in red in the previous image ).

-(BOOL)tableView:(NSTableView *)tableView isGroupRow:(NSInteger)row
{
    DesktopEntity *entity = _tableContents[row];
    
    if ([entity isKindOfClass:[DesktopFolderEntity class]])
    {
        return YES;
    }
    
    return NO;
}

and here's my tableView:viewForTableColumn:row: method where I have two if statements to decide whether the current row is a group row (meaning it's a folder) or an image:

-(NSView*)tableView:(NSTableView *)tableView viewForTableColumn:(NSTableColumn *)tableColumn row:(NSInteger)row;
{
    
   
    DesktopEntity *entity = _tableContents[row];
    

    if ([entity isKindOfClass:[DesktopFolderEntity class]])
    {
        NSTextField *groupCell = [tableView makeViewWithIdentifier:@"GroupCell" owner:self];
        [groupCell setStringValue: entity.name];

        [groupCell setFont:[NSFont fontWithName:@"Arial" size:40]];
        [groupCell setTextColor:[NSColor magentaColor]];
        return groupCell;
    }
    else if ([entity isKindOfClass:[DesktopImageEntity class]])
    {
        NSTableCellView *cellView = [tableView makeViewWithIdentifier:@"ImageCell" owner:self];
        [cellView.textField setStringValue: entity.name];
        [cellView.textField setFont:[NSFont fontWithName:@"Impact" size:20]];
        [cellView.imageView setImage: [(DesktopImageEntity *)entity image]];
        return cellView;
    }
    
    return nil;
}

Now, if the current row is an image, I change its font to Impact with a size of 40 and that works perfectly, the problem here is with the first IF statement, for a group row I wanted to change the font size to arial with a size of 40 with a magenta color but for some reason I can only get the color to work:

You can see that my changes to the font size didn't work here, what gives?

How can I change the font size for the group row ?