Is it possible to create a subdomain with a different system user than the subscription?
By default, all subdomains and domains under the same subscription share the same system user and main directory.
Yes, it’s possible. Instead of creating a subdomain out of a domain from Plesk, it can be accomplished by creating a new separate subscription with the subdomain name:
Go to Subscriptions > Create New Subscription.
Specify a subdomain name as the name of the new subscription. For example:
Note: after creating subdomain as a subscription, it is required to register the name
one.example.com on the Registrar side.