If the docker update doesn't update things you might not be using docker at all. Docker is like having a VM that you destroy after every run, so it's not that it updates the version, it is as if you were spinning up a new machine with the new version, a machine running the new version can't be running the old version by definition, unless you did something like telling that machine to overwrite the installation folder with a local one, e.g. by having something like - /var/www/nextcloud:/var/www/nextcloud (or whatever the path is where you have next cloud installed locally) in your volumes for the docker, which would be akin to buying a new PC because your GPU is old, immediately swapping out the new GPU for the old one, and wondering why the new GPU is so slow.