Adding a Nextcloud calendar to Thunderbird
Thunderbird is our favourite email client for many reasons, but the most important one is this: Thunderbird is open source and independent of big tech, which makes it very privacy-friendly.
In Thunderbird you can easily connect the mailboxes from your hosting package (read Adding an email address to Thunderbird), and you can also add your Nextcloud calendar in just a few clicks.
Step 1 - To add your calendar to Thunderbird you need an app password. Your regular password won't work here. You can read how to create an app password in Creating an app password (needed to connect with apps and devices).
Step 2 - Open Thunderbird and click Calendar in the bar on the left. Then click New Calendar... at the bottom left.
Step 3 - Choose On the Network and click Next.
Step 4 - Under Username, enter the username of your Nextcloud account, and under Location enter https://jouw-adres/remote.php/dav. Replace jouw-adres with the address you use to open your Nextcloud in the browser, for example yourname.webokecloud.nl or cloud.yourcompany.com. Then click Find Calendars at the bottom right.
Step 5 - If Thunderbird asks for a password, enter the app password you created in step 1 and tick the box that allows Thunderbird to remember it.
Step 6 - You'll now see all the calendars and task lists your Nextcloud account has access to, including calendars others have shared with you. Tick the ones you want to add to Thunderbird and click Subscribe.
Step 7 - Done! Your calendar is now connected to Thunderbird. Every appointment you add, delete or edit here is synchronised with your Nextcloud right away, and vice versa. When creating a new appointment, make sure you select your Nextcloud calendar and not a calendar On My Computer.
Not working? If you get "The credentials you entered were not accepted", check your username and make sure you're using the app password. If Thunderbird says no calendars were found, check the location: it starts with https:// and ends with /remote.php/dav.
Detailed explanation with screenshots: Adding your Nextcloud calendars and task lists and Adding your Nextcloud contacts in the Thunderbird manual.