Node-RED is opensource and free. ( and is not made by me, but OpenJS Foundation )
You can start Node-RED using an agent.
You can start agents on any computer running linux/macos or linux either on the desktop using the assistent or as a deamon or start it as a docker instance on docker or as a deployment inside kubernetes.
The last one, requires a license ( the agent provider for kubernetes has not been made open source everything else is )
So if you want to run this on premise or in your own cloud, you need
docker if you want to run pure open source and without a license.
you need a premium license to deploy it on kubernetes or openshift. ( you can deploy it, but you cannot start any agents )