I don't know if someone still needed this, but the alternative I found is using panel, then setting the BorderStyle to FixedSingle, then height to 2px. You can also do it with vertical separator lines using same method except the width set to 2px instead of the height. I was used to designing layout on Netbeans with Java using javax.swing.Separator and I was looking for it when I shift language to C# with Visual Studio 2022.