What’s the problem with just not using the portion of the service you do not wish to use? For almost everyone, the integration with email for the calendar is what actually makes it function, where you will be interacting with other people. Most people who want to create a new, unique calendar will just create an additional one in an existing account if they want a separate calendar for a certain purpose.
That’s what I do with my wife for events that we both need to know about. So we have a calendar that is just our stuff and we both subscribe to it (or more like she has the calendar shared with her from my account) but she has permissions to add/remove things. Is there some reason you need a completely separate calendar on a unique service? I feel like we are missing something about your use case to actually be able to understand what you are trying to do.
If she woke up to a vibration from a watch, I bet she’d wake up hearing motorized blinds.