Looking for some guidance on best practices for what can be outputs of a custom ComponentResource. More specifically how should one share a resource created by the component resource so it can be referenced from a different project / stack. Can resource object be an output? Case in point: Project A uses custom ComponentResource to provision a complex set of resources including a public IP address (in Azure). We want to reference this public IP address resource in a different project for registration in DNS / firewall / etc. What should the output property be?

I always avoid this by passing only the required IDs around (the IDs of the constituent resources). But in theory you could either marshal and unmarshal the ComponentResource youself, or provide a "read-only" flag and write code that gets all the constituent resources, instead of newing them.

If I understand correctly you are suggesting returning "native" ID of the created resource and using GetXyz to retrieve the resource elsewhere.

Yes, that's one way of doing it. Or just storing the IDs, and deferring retrieving until it's actually needed. It often isn't: in a lot of cases, only the IDs of the resources are ever used.