Let me see if I can explain, in terms of the community both adobe and intuit have shared quite a bit how they have built their idp`s, there have been smaller ones but the information is limited, what I mean by that is like you said a IDP is just not the architecture/tools, its also how they worked their processes around it, how they do their local environments and how that relates to the IDP, best practices they found useful etc, when it comes to companies that are selling a IDP platform or even open source ones, they focus more on the tooling ( because well their selling a tool ), but not so much the rest ( local environment setup, best practices etc, although im sure if you purchase their platform/product they will be happy to share best practices with you 😂 ) if that makes sense, the only one I know of that has shared best practices, how local environments would work with it etc is
https://www.getambassador.io/ ( but thats because their building a tooling ecosystem around it )