In the Docker installation there’s no “SSL Setup” option as opposed to the, for instance, Ubuntu one. So I cannot choose the “auto” option to issue a SSL certificate through Let’s Encrypt.
Does anyone know if there’s a method to do such a thing via Docker?
Indeed the passbolt docker container doesn’t provide any let’s encrypt capabilities. However you could potentially place a reverse proxy in front of it that does this for you (there are several docker reverse proxies that do this for you), or you could use the official certbot docker image to retrieve the cert and place it on a shared volume for the passbolt container.