That's so strange... I wonder what and how it's determined to be healthy or not. If you can login to the container, I'd say it's up and running. You'll likely want to customize it if you access the environment from outside of docker though. The docker (not compose) example and/or this other recent thread will probably be important to you. They show the environment variables that are needed to customize the docker environment for external addresses so the config files are generated for proper configuration outside the docker network. Looking at the docker .env file there might be one or two env vars missing in there that you'll probably have to add. I must admit I've not used the docker-based quickstarts for a while to recall how much effort there will be to get them working more generically. hopefully the other discourse posts and doc will make it clear and you'll find what you need.
I don't have a proxmox setup, but this issue makes me want to try it out to see if there is something proxmox does to (falsely?) report a failure when bringing up the project?