Currently, support for integration with an external (i.e. not operated by /e/ Foundation) Nextcloud server is somewhat of a hidden feature. The process is to enter the location of the Nextcloud instance in a field provided in the form for creating an /e/ Cloud account.
This flow is confusing, especially for anyone new to the design.
I suggest that a clearer flow would be to separate the builtin account types of /e/ Cloud and Nextcloud, with the difference that the user provides the server name for the Nextcloud account, whereas the server name is always implicit for an /e/ Cloud account.
Ultimately, the characterization of an arbitrary Nextcloud account as an /e/ Cloud account with a custom server name relies on semantics that are not accurate in general use, and therefore require extra learning of the /e/ OS design in order to utilize effectively. From a standpoint of general users, it is a design detail that /e/ Cloud is implemented as a Nextcloud deployment.