Uno Platform is a cross platform implementation of the WinUI+WinRT APIs. That cross-platform implementation never used the official WinUI/WinAppSDK implementation on Windows.
When running on Windows, which this is where some confusion may lie, you can choose to use the Uno implementation (the netX.0-desktop TFM), or the original WinAppSDK by Microsoft (the netX.0-windows10.YYY TFM), since both implementations share the same API, making user code compatible with either ones.
On the other platforms, Wasm/Linux/iOS/Android/Catalyst/macOS, only the Uno implementation can be used.
When running on Windows, which this is where some confusion may lie, you can choose to use the Uno implementation (the netX.0-desktop TFM), or the original WinAppSDK by Microsoft (the netX.0-windows10.YYY TFM), since both implementations share the same API, making user code compatible with either ones.
On the other platforms, Wasm/Linux/iOS/Android/Catalyst/macOS, only the Uno implementation can be used.