To continuously update the PowerShell title bar, and for example display the current date and time, you need a background thread that takes care of this. Without a background thread, your PowerShell would be busy all the time updating the title bar, thus unusable.
Here is a simple piece of code you can run to display a live clock in your title bar:
# submit the host process RawUI interface and the execution context
# compose the time and date display
$time = Get-Date -Format 'HH:mm:ss dddd MMMM d'
# compose the title bar text
$title = "Current Time: $time"
# output the information to the title bar of the host process
$RawUI.WindowTitle = $title
# wait a half second
Start-Sleep -Milliseconds 500
} while ($true)
$ps = [PowerShell]::Create()
$null = $ps.AddScript($code).AddArgument($host.UI.RawUI)
$handle = $ps.BeginInvoke()
The crucial thing here is to pass over the $host.UI.RawUI object from your foreground PowerShell to your background thread code. Only then can your background thread access the title bar owned by your foreground PowerShell.
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Here are two additional posts on this type of use case.