Future Windows Updates permanently broken

September’s Patch Tuesday for Windows 11 24H2 introduced “checkpoint cumulative updates” for Copilot+ PCs — a new servicing model that promptly broke the ability to install any future updates. Systems that had added Feature on Demand or Language Packs from local sources on top of the checkpoint update would fail all subsequent updates with “Operation is not supported” errors. The fix was to manually re-download and reinstall KB5043080 from the Microsoft Update Catalog, which really drives home the irony of Windows Update breaking Windows Update.