Apple rolled out a new version of iTunes for Windows on Monday alongside iOS and iPadOS 15, but it should be avoided at all costs if your system isn’t set up in English. iTunes no longer works under any other language.
The problem seems to affect the version 12.12.0.6 version of iTunes no matter where it’s downloaded from — the Microsoft Store or directly from Apple — which means it’s not currently possible for some users to sync their devices.