I created a super-simple CalDav-esque web endpoint in my personal website that receives HTTP requests from a command line tool, stores the calendar events, and then returns them as a dynamic ICS file. Then, I use Apple’s Calendar app to subscribe to a “hidden” URL and iCloud automatically distributes the subscription to all my devices.
It sounds super dumb but it works so well.
The main feature is that I can categorize the events (personal, family, work, friends, etc.) and share individual URL’s with other people. Admitedly, I didn’t try solving this problem with Google Calendar, Apple Calendar, or any other calendar service, mostly because I wanted to own my data and also learn a bit more about CalDav itself.