I have seen a few "great" deployments of Backstage, but I would say these are largely few and far between. Unfortunately, I am unable to find public talks/video/docs for some of the great ones I have seen. What I can say is that those instances have required full, dedicated teams to manage these portals at scale, usually in-house but may also be possible through a managed Backstage provider.
(Full disclosure: we built a managed Backstage offering that we have recently EOL'd in favor of a new fully-customizable, AI-first approach)
I suspect that this could be the reason there are so few "great" publicly-available deployment examples: teams want what Backstage can offer, but find it extremely difficult to deploy, customize, and maintain. And, further, find it even harder to dedicate resources to that work. So, most end up with a very "stock" look/feel that may very well become limited by their own ability to service it.