avoid interaction installing xfce

[david]

Folks

I am trying to install xfce4-session in a several Ubuntu 20.04 LTS 
servers, some physical, some virtual.  These are fresh installs.  The 
install is driven from a Perl script, containing the following (as root):

$ENV{DEBIAN_FRONTEND} = 'noninteractive';
system( "apt -y -qq install xfce4-session" );

Apparently this install requires intervention from the user, under 
the title of "Package Configuration" and thus assumes there's a 
console.  In this case, there is no one present.  I really don't want 
to go to each of them and interact with the installation sequence by 
hand..  Is there some way to avoid the interactive process in the 
install?   Any clues?

Thanks

David