Hi João,
yes, as soon as you activate the user, it counts as an additional licence and would therefore also incur monthly costs.
However, there is a way to avoid this issue and register as an inactive _system_user; however, this requires a basic adjustment per Odoo instance and should be taken into account directly when setting up new instances if you want to save yourself separate manual effort later.
Odoo has its own function for logging in as an administrator in the system as a SuperUser - the _system_user is then accessed here, even if it is actually archived. In the browser, you can switch to SuperUser mode as a logged-in admin either via ‘[domain_name]/web/become in the URL or via the developer mode and then the beetle that appears at the top - as you can then see, your account becomes the _system_user or OdooBot user.
So that it is not necessary to log in to the system as an administrator beforehand, the function for /web/become must be overwritten (I can provide code if required). In the function, a login as administrator is then executed and /web/become is called directly, so that you immediately log in as _system_user when connecting.
A password for the _system_user is then not necessary - but you can set a password on the system side as with an htaccess (independent of the password in Odoo - this is not used).
Note: if you log in as _system_user, you still do not have all rights and functions in the system, even if this appears to be the case at first - for example, you cannot open a Point of Sales session as _system_user, as this requires an active user in the system. This should at least be taken into account in the support section, as not everything is possible after all
Regards,
Chris Dominiak (Intero Technologies GmbH)