For example with the web the interoperability is really between the browser and websites rather than between websites. Although a few do interoperate. This is more similar to how Roblox or Steam works where one program lets you join lots of different games and maintains some common state than common ideas of interoperability in the metaverse.
I think the Zuck use case was buying a t-shirt for a virtual avatar and I want to use that t-shirt in other applications. There is a matter of interoperability required at the level of the data that sits behind both applications as it pertains to the user that sits on the other side of those applications. (meaning just sharing data isn't enough, there is user level context as well).
And if you reduce interoperability to a single entity owned platform (like Steam), well other platforms will exist and the interoperability problem will be recreated.
To me the issues that require addressing are things like standardization, general uniqueness proofs, Cross-app total order broadcast, identity and service discovery, to just name a few.
My feeling is that the internet does not solve these problems, especially at the application layer, and therefore interoperability is a technical solution that is required for a metaverse like vision.
I believe the path to those soltuons does lie on the road of ubiquitous and dynamic technical interoperabity for web applications.