I would like to be able to maintain a calendar privately, using offline calendar applications on both my Android mobile and Windows/Linux desktop computers.
I understand that cloud services tend to scrape events from any user's hosted calendars for various reasons, including providing recommendations to the user.
However, in avoiding cloud services, there is a manual effort in copying ics files via a local connection and merging changes periodically.
Are there any popular methods to sync a calendar file privately between platforms, with or without the use of cloud services?
For instance, it is possible to encrypt the calendar, host it on a domain, and to access from both sides via SFTP. It might also still be possible to use existing services here - say by syncing a locally encrypted calendar with a private key not known to Google.
So I would like to know either if there are existing implementations of this or if anyone has suggestions of alternative approaches.