In fact, none or almost none of the IO-related methods are implemented. Documentation also says that directly at https://doc.qt.io/qtforpython-6/PySide6/QtAsyncio/index.html:

We consider that this API consists of two levels:

1. Fundamental infrastructure for event loops and asynchronous operations, including futures, tasks, handles, executors, and event loop management functions (see below).
2. A user-facing API for use in applications, including transports and protocols, network connections, servers, sockets, signals, subprocesses.

QtAsyncio currently covers the first level.:

One solution is to use trio in guest mode, like in this example: https://doc.qt.io/qtforpython-6/examples/example_async_minimal.html. Except it will not help you, because LangChain does not support trio. There are a few libraries that implement a similar capability for asyncio, but none of them seem particularly mature.