The minimal program to reproduce the issue:

import uasyncio as asyncio

f = asyncio.ThreadSafeFlag()

async def main():
    await f.wait()

asyncio.run(main())

The result:

Traceback (most recent call last):
  File "t.py", line 8, in <module>
  File "/usr/lib/micropython/uasyncio/core.py", line 222, in run
  File "/usr/lib/micropython/uasyncio/core.py", line 191, in run_until_complete
  File "/usr/lib/micropython/uasyncio/core.py", line 176, in run_until_complete
  File "t.py", line 6, in main
  File "/usr/lib/micropython/uasyncio/event.py", line 57, in wait
  File "/usr/lib/micropython/uasyncio/core.py", line 94, in queue_read
  File "/usr/lib/micropython/uasyncio/core.py", line 79, in _enqueue
TypeError: can't convert NoneType to int

I poked around it a bit, and the flow to the failure is as follows:

https://github.com/micropython/micropython/blob/cb99ca9862827f57c370555841810e98701ecfa2/extmod/uasyncio/core.py#L79

https://github.com/micropython/micropython/blob/cb99ca9862827f57c370555841810e98701ecfa2/ports/unix/moduselect.c#L88

https://github.com/micropython/micropython/blob/cb99ca9862827f57c370555841810e98701ecfa2/ports/unix/moduselect.c#L76

This ends up in ThreadSafeFlag.ioctl(), which returns None for any request other than MP_STREAM_POLL and causes the exception above.

https://github.com/micropython/micropython/blob/cb99ca9862827f57c370555841810e98701ecfa2/extmod/uasyncio/event.py#L47-L50