Thank you @Andy_Wismer for your quickly and detailed answer!
Actually, I want to provide Nextcloud services only for my company (suggested site: cloud.mycompany.tld), using NS Nextcloud module. It works like that with @giacomo solution. So, I don’t need Nextcloud as multisite/multiple domains.
For sites based WP is another discussion, but here:
HowTo install Wordpress on NethServer
Of course, my Q&A will be based on NS Virtual hosts.
Gabriel