PowerShell GUI containing multiple ListBoxes

I am trying to modify the code found in the Microsoft Documentation (https://learn.microsoft.com/en-us/powershell/scripting/samples/multiple-selection-list-boxes?view=powershell-7.2) to contain 2 ListBoxes: One single select, and one multiple selected.

This issue is only listBox2 is showing up. What I have so far:

Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing

$form = New-Object System.Windows.Forms.Form
$form.Text = 'Data Entry Form'
$form.Size = New-Object System.Drawing.Size(600,200)
$form.StartPosition = 'CenterScreen'

$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Location = New-Object System.Drawing.Point(75,120)
$OKButton.Size = New-Object System.Drawing.Size(75,23)
$OKButton.Text = 'OK'
$OKButton.DialogResult = [System.Windows.Forms.DialogResult]::OK
$form.AcceptButton = $OKButton
$form.Controls.Add($OKButton)

$CancelButton = New-Object System.Windows.Forms.Button
$CancelButton.Location = New-Object System.Drawing.Point(150,120)
$CancelButton.Size = New-Object System.Drawing.Size(75,23)
$CancelButton.Text = 'Cancel'
$CancelButton.DialogResult = [System.Windows.Forms.DialogResult]::Cancel
$form.CancelButton = $CancelButton
$form.Controls.Add($CancelButton)

#Single Select Start

$label = New-Object System.Windows.Forms.Label
$label.Location = New-Object System.Drawing.Point(10,20)
$label.Size = New-Object System.Drawing.Size(280,20)
$label.Text = 'Select Primary USB from the list below:'
$form.Controls.Add($label)

$listBox = New-Object System.Windows.Forms.Listbox
$listBox.Location = New-Object System.Drawing.Point(10,40)
$listBox.Size = New-Object System.Drawing.Size(260,20)

#Single Select End

#Multiple Item Select Start

$label2 = New-Object System.Windows.Forms.Label
$label2.Location = New-Object System.Drawing.Point(310,20)
$label2.Size = New-Object System.Drawing.Size(280,20)
$label2.Text = 'Select Secondary USB(s) from the list below:'
$form.Controls.Add($label2)

$listBox2 = New-Object System.Windows.Forms.Listbox
$listBox2.Location = New-Object System.Drawing.Point(310,40)
$listBox2.Size = New-Object System.Drawing.Size(260,20)

$listBox2.SelectionMode = 'MultiExtended'

#Multiple Item Select End

$testArray = gdr

ForEach($n in $testArray){
    if(($n.Root.Length -lt 4) -And ($n.Root.Length -gt 0) -And ($n.Root -ne "\") -And ($n.Root -ne "C:\")){
        [void] $listBox.Items.Add($n.Root)
        [void] $listBox2.Items.Add($n.Root)
    }
}

$listBox.Height = 70
$listBox2.Height = 70
$form.Controls.Add($listBox1)
$form.Controls.Add($listBox2)
$form.Topmost = $true

$result = $form.ShowDialog()

if ($result -eq [System.Windows.Forms.DialogResult]::OK)
{
    $x = $listBox1.SelectedItem
    $y = $listBox2.SelectedItems
    Write-Host "Single Item Selected" $x
    Write-Host "Multiple Items Selected" $y
}

P.S. Can someone please make a new tag for PowerShell-GUI