Plus, from reading that doc, it sounds like it only works on Windows if you enable “App-Local ICU” mode, in which case the ICU DLL is added to your .Net app’s distributable package - which implies the info isn’t actually bundled with Windows itself

Consider Python’s zoneinfo standard library module-it provides access to IANA TZ database. On all platforms except Windows it uses the copy of the DB bundled with the OS and updated by the OS update mechanisms. On Windows, you have to install a PyPI module containing it. If Microsoft bundled it with the OS, with a C (not .Net) API, you wouldn’t have to do that-but Microsoft doesn’t, so you do