Example of how to wait for a scheduled task to finish running

WaitForScheduledTaskExample.ps1

$Trigger = New-JobTrigger -Once -At (get-date).AddSeconds(5)
$JobOptions = New-ScheduledJobOption -StartIfOnBattery -RunElevated
$Job = Register-ScheduledJob -Name "TaskName" -Trigger $Trigger -ScheduledJobOption $JobOptions `
  -ScriptBlock {
    Sleep 5
  }

# From https://docs.microsoft.com/en-us/windows/win32/taskschd/task-scheduler-error-and-success-constants?redirectedfrom=MSDN
Set-Variable -Name "SCHED_S_TASK_HAS_NOT_RUN" -Value 0x00041303 -Option Constant
Set-Variable -Name "SCHED_S_TASK_RUNNING" -Value 0x00041301 -Option Constant
Set-Variable -Name "SCHED_S_TASK_SUCCESS" -Value 0x0 -Option Constant
do {
  Sleep 1
  $ResultCode = (Get-ScheduledTask -TaskName "TaskName" | Get-ScheduledTaskInfo).LastTaskResult
  switch ($ResultCode)
  {
    $SCHED_S_TASK_HAS_NOT_RUN { Write-Host "Waiting to run the task" }
    $SCHED_S_TASK_RUNNING { Write-Host "Task is running!" }
    $SCHED_S_TASK_SUCCESS { Write-Host "Task completed" }
    default { Write-Host "Error! $ResultCode" }
  }
} while (@($SCHED_S_TASK_HAS_NOT_RUN, $SCHED_S_TASK_RUNNING) -contains $ResultCode)

$Job | Unregister-ScheduledJob