Thunderbird ↔ Nextcloud Calendar and Task Sync

1️⃣ Enable CalDAV on Nextcloud

• Log in to your Nextcloud web interface.
• Go to Settings → Calendar.
• Under CalDAV copy your calendar and task URLs (they look like https://workspace.yourdomain.com/remote.php/dav/calendars/username/personal/).

2️⃣ Add the Calendar to Thunderbird

• Open Thunderbird → Calendar tab.
• Click + New Calendar → On the Network → choose CalDAV.
• Paste the Nextcloud CalDAV link you copied.
• Enter your Nextcloud username and password (or app password if 2FA is on).
• Name the calendar (e.g., “Nextcloud Work”) and choose a color.

✅ All your Nextcloud events and tasks will now appear inside Thunderbird.

3️⃣ Add Tasks (To-Do Sync)

• Thunderbird’s “Tasks” panel uses the same CalDAV calendar.
• Ensure Tasks are visible under View → Tasks Pane.
• Any task created here will sync both ways with Nextcloud’s “Activity⚡” and Thunderbird’s “Tasks”. 

4️⃣ Optional: Contacts Sync

• In Thunderbird, install CardBook (Add-ons → search for “CardBook”). 
• Add an address book via CardDAV using your Nextcloud contacts URL. 
• In Nextcloud, open the Contacts app. Click ⚙️ Settings → copy the CardDAV link. 
• In Thunderbird: Click Address Book (top-left). Add-ons → search for CardBook → install it. 
• After restarting, open CardBook → click New Address Book → Remote → CardDAV. 
• Paste the link and enter your username and password.

✅ Your Nextcloud contacts sync automatically.

5️⃣ Verify Sync

• Create a test event and task in Thunderbird.
• Check the Nextcloud Calendar and Tasks apps to confirm they appear.
• Repeat in reverse (Nextcloud → Thunderbird).