no method "ListDirectory"

This does not work per https://winscp.net/eng/docs/library_session_listdirectory:

$directory = $session.ListDirectory("/home/martin/public_html")

Method invocation failed because [System.Boolean] does not contain a method named 'ListDirectory'.

I'm using WinSCP v.5.13.4 Build 8731

Your example does not show, how do you initialize the `$session` variable.