^ The Accompanist libraries are “official” in that they are developed by the folks at Google. They’re usually put there for unstable APIs that they’re still working on which they intend to eventually move into the core Compose library (insets, FlowLayout, and ViewPager, for example). The APIs that get promoted to Compose core are typically supported on all Compose targets.
It’s also where they keep artifacts that are more “extras”, especially ones tightly coupled to the Android system (such as theme adapters and navigation). WebView falls into this category, so I wouldn’t expect it to get promoted to the core Compose libraries.
Not to mention, it would be a huge challenge to make it work on all targets, since some like Desktop, don’t have any good option for WebViews yet, let alone something that could be bridged to a common API.