Powershell: Show GUI Messagebox and wait for user input or timeout

Show-MessageBox.ps1

<#
.SYNOPSIS
    Show GUI Messagebox
.DESCRIPTION
    Show GUI Messagebox and wait for user input or timeout
.PARAMETER Message
    Message to show
.PARAMETER Title
    Messagebox title
.PARAMETER Buttons
    Messagebox buttons
.PARAMETER Icon
    Messagebox Icon
.PARAMETER Timeout
    Messagebox show timeout in seconds. After that it will autoclose
.EXAMPLE
    PS C:\> Show-MessageBox -Message 'My Message' -Title 'MB title' -Buttons = 'YesNo' -Icon Information
    SHow Messagebox with message, title, Yes/No buttons and Information icon
.EXAMPLE
    PS C:\> Show-MessageBox -Message 'Everything Lost !' -Title 'This is the end' -Icon Exclamation -Timeout 10
    SHow Messagebox with message, title, Exclamation icon with 10 sec timeout
.OUTPUTS
    System.Windows.Forms.DialogResult. If timed out, return No
.LINK
    https://stackoverflow.com/a/26418199
    https://docs.microsoft.com/ru-ru/dotnet/api/system.threading.tasks.task.delay?view=netframework-4.5    
.NOTES
    Author: Max Kozlov
    Idea from stack overflow
    Required Net 4.5+
    TODO: set focus on messagebox window
#>
function Show-MessageBox {
[CmdletBinding()]
param(
    [Parameter(Mandatory, Position=0)]
    [string]$Message,
    [Parameter(Position=1)]
    [string]$Title = '',
    [ValidateSet('OK','OKCancel','AbortRetryIgnore','YesNoCancel','YesNo','RetryCancel')]
    [Parameter(Position=2)]
    [string]$Buttons = 'OK',
    [ValidateSet('None','Hand','Error','Stop','Question','Exclamation','Warning','Asterisk','Information')]
    [Parameter(Position=3)]
    [string]$Icon = 'None',
    [Parameter(Position=4)]
    [int]$Timeout = 0
)
    Add-Type -Assembly System.Windows.Forms
    $w = $null
    if ($Timeout) {
        $cancel = New-Object System.Threading.CancellationTokenSource
        $w = New-Object System.Windows.Forms.Form
        $w.Size = New-Object System.Drawing.Size (0,0)
        [System.Action[System.Threading.Tasks.Task]]$action = {
            param($t)
            Write-Debug "Want to Close $($task.Status)"
            $w.Close()
        }
        $task = [System.Threading.Tasks.Task]::Delay(
            [timespan]::FromSeconds($Timeout), $cancel.Token
        ).ContinueWith($action,
            [System.Threading.Tasks.TaskScheduler]::FromCurrentSynchronizationContext()
        )
        Write-Debug "Before $($task.Status)"
        #$w.TopMost = $true
        #$w.Modal = $true
        $w.Show()
        $w.Left = -10000
        $w.Top = -10000
        $w.Focus()
    }
    [System.Windows.Forms.MessageBox]::Show($w, $Message, $Title, $Buttons, $Icon) #Topmost
    if ($Timeout) {
        Write-Debug "After $($task.Status)"
        if ($task.Status -ne 'RanToCompletion') {
            Write-Debug "Do Cancel"
            $cancel.Cancel()
            $task.Wait()
            $cancel.Dispose()
        }
        $task.Dispose()
    }
}

I had to add:
$w.TopMost = true;
$w.Focus();
$w.TopMost = true;
from https://stackoverflow.com/a/47850889
I don't know if less would have worked

@maxsieber,
the focusing problem is that $w is the parent window, and the messagebox is the child window that should be focused
but main widow ($w) is hidden.

@maxsieber !
Thanx, you give me the clue :))
show() is the key

The focus problem seems solved now