XDM is supported but unfortunately at the moment that is a problem affecting the functionality,
described here https://www.nomachine.com/TR11K04020.
Server administrators can also add XDM login as a mandatory login method for specific groups of users.
In the meanwhile we are also investigating how the functionality can be improved, for example
to better integrate with the host environment.
Regarding Xwillings, as far as we know, this file is only used by XDM, while we would like to
offer a wider range of choices.
We believe that (once the bug will be fixed) the ability of the administrator to set the XDM login
command on the server will give people the best flexibility and adapt to most setups.