Thanks Jean, those commands produced a change but not a fix.
I now get:
FILE NOT FOUND
The requested resource was not found!
Please contact your server-administrator.
Failed request: 172.16.16.73/roundcube/
It is now showing as enabled:
roundcube=service
DbName=roundcube
DbUser=roundcube
Name=RoundCube IMAP Client
PluginsList=globaladdressbook,contextmenu,markasjunk,vcard_attachments,newma il_notifier,emoticonss,managesieve,nextcloud_attachments
access=public
status=enabled