Environment variable “NEXTCLOUD_UPDATE”
Your docker container needs to have set the environment variable “NEXTCLOUD_UPDATE” to “1”. Without set, you won’t receive any updates when you update the container.
Why does the web updater not work?
When you go to settings -> overview -> update, you will be redirected to the dashboard or the index of your nextcloud web address. This is because the underlying nextcloud docker image does not include the updater scripts. This is by purpose, not by mistake. You should not update the web app, you should always update the container. By that nextcloud ensures that the container ships everything the nextcloud version needs (e.g. a specific PHP version).
So, always update the container to receive a new version of nextcloud.
How often do you update the docker image?
As soon as nextcloud releases a new version, I update my container, too.