I followed the guides here in the forum and by TechnoDadLife to set up Let's encrypt with Nextcloud, as DDNS-provider I'm using MyFritz. In the settings of my FritzBox it's possible to use certificates from let's encrypt automatically for my MyFritz address (something.myfritz.net), I've activated it and it does work if I'm accessing my FritzBox from outside via https://something.myfritz.net:1234.
I then created a port release for Nextcloud and linked it to MyFritz which worked as well, I can reach my Nextcloud now via myNAS.something.myfritz.net:444. However, the let's encrypt certificate I created before obviously doesn't include this subdomain thus I'm getting a warning message when accessing. Firefox says the certificate comes from linuxserver.io. Further on I set up the letsencrypt-docker, according to docker logs -f letsencrypt everything seems to work, no errors reported. I set the domain to something.myfritz.net and subdomain to myNAS and Let's encrypt seems to create a certificate for myNAS.something.myfritz.net indeed, but when accessing my Nextcloud nothing has changed, the certificate is still not trusted and comes from linuxserver.io. Does anyone have a clue how to get this work?