After many attempts to eliminate the “custom integration needs to be installed in Home Assistant for this node to function correctly” error (upgrading to v7 finally did the trick) I have no errors listed in Node-Red on the Entity Node I’m experimenting with.
I must be missing something however, because after deploying the flow I do not find a new entity to work with in HA.
Node-Red is running as an add-on, and the Node-Red Companion Component was installed with HACS. It is listed as an installed integration.