- Create an app-specific password for iCloud account (check Bitwarden notes)
- Use https://github.com/midnightmonster/icloud-calendar-urls to get your calendar's secret URL
curl -s https://raw.githubusercontent.com/midnightmonster/icloud-calendar-urls/master/icloud_calendar_urls | bash
- In thunderbird, add calendar with your icloud username, secret url and app-specific password