Although I already added an exception for the SSL certificate of my Nextcloud server, I keep getting the errors below when trying to add the CalDAV / CardDAV account. Can anybody let me know what I am doing wrong?
You haven’t provided enough information, especially about your self signed certificate.
The error message explicitly states you need to import the cert into Thunderbird - have you done that? You only state you’ve “added an exception for the SSL certificate of my Nextcloud server”. It’s not clear if you mean your browser has an exception for your Nextcloud, or if you actually added the cert to Thunderbird.
Also, is your self signed cert for an IP address or for a domain name? It matter which you’ve chosen.
Lastly, you really need to understand how certificates work. SSL certificates are fundamentally broken, the protocol was last updated in 1996, and was officially depreciated in 2015. Chances are you’re using a TLS certificate, but generated by OpenSSL?
By not filling out the support template, you’ve made it very difficult for us to help you.
Edit: I just noticed the URL you’re using to connect to CalDav. It contains “.well-known”. That’s REALLY wrong. Are you using a self signed certificate? Or are you using Let’s Encrypt? Jesus dude, the lack of information in your post is frustrating. Let’s Encrypt uses the “.well-known” token to update a certificate.