I have a question. I have a desktop computer with Ubuntu 16.4 installed. What I want is that I want to synchronize my appointments /to do list and all my contacts from my android (LineageOS) mobile phone via Davdroid with Thunderbird on my PC. For this I have installed Nextcloud Server 12.0.2 on my PC. Now, my question is whether you would use ssl/tls for this,
Keep in mind that Davdroid doesn’t like working with self signed certificates, so I’d recommend using a certificate from a Certificate Authority (CA). Let’s Encrypt is a free CA that has multiple options for certificate update clients that’ll work on Ubuntu.
You didn’t mention whether you have a domain or not. CAs can only issue certificates for domains, not IPs. You should definitely use TLS, but you’ll need a domain. Just get a free one if you need to. (I’m using a free .tk domain.)
Also, just as a reminder, you configure TLS in your webserver (Apache/Nginx), it’s not a Nextcloud setting.
Like you, I’m syncing my phone (Cyanogenmod) calendar and contacts with Thunderbird (Lightning and Cardbook). After getting it working unencrypted, I then got it working with self signed certs. Self signed certs are a pain though, and lots of apps refuse to work with them, so I switched to Let’s Encrypt once they went public.