Ah! now I see the problem

permission denied, mkdir ‘upload/library’

It’s clearly having permission problems with the image library directory.

Also:

volumes:
 - /mnt/NAS-immich-folder:/mnt/immich
 - ${UPLOAD_LOCATION}:/mnt/immich

with this command you are trying to mount this directory from your LXC machine:

/mnt/NAS-immich-folder

into this directory inside the immich container:

/mnt/immich

And then you also try to mount a second directory there in the next line. But immich doesn’t use /mnt/immich for its library, it uses this:

/usr/src/app/upload

You should NOT edit the default docker-compose.yml file. Instead you should only edit the .env file like so:

UPLOAD_LOCATION=/mnt/NAS-immich-folder

I can also see that there’s a specific tutorial on how to set it up with portainer. In that case you might have to edit the docker compose file to replace .env with stack.env and place the contents of the env file in the advanced-> environment variables of portainer.

Try these things and ask here again if you can’t get it running.