the read-only use-case should work. Nextcloud exports a valid iCal / vcalendar v2.0 endpoint on click to “Copy subscription link”
https://murena.io/remote.php/dav/public-calendars/<auth-secret>?export
the edit permission is more difficult and only possible if the user has an account on the same server - Share calendar with other /e/OS users
If it’s family might be worth it to get them all accounts