Ask HN: How do you manage your calendars?

I'm trying to find a simple open source way to keep all my calendars from different sources like work, university, organizations, and private synced together

On the phone I'm using "simple calendar" and on the computer I'm using "Kalendar", each subscribing to different organization calendars separately, making it a mess. Adding new private events to each obviously won't show on the other

Is there something small and simple I could host on my home server or something that subscribes to each of the external calendars, backs up the events, and generates a subscription link I could use on my client apps on the phone and computers?

One alternative would be to use google calendar and their subscribe to calendar feature but I'd very much rather not, that would be a last resort

How have you all solved the management of your calendars?