There is no documentation indicating that ngrok.forward can return an _asyncio.Task.

Running this code:

import asyncio
import ngrok
NGROK_TOKEN = ""

def sync():
    listener = ngrok.forward(80, authtoken=NGROK_TOKEN)
    print("sync")
    print(type(listener))

async def async_():
    listener = ngrok.forward(80, authtoken=NGROK_TOKEN)
    print("async")
    print(type(listener))

    print("async calling sync..")
    sync()

sync()
asyncio.run(async_())

Gives this output:

sync
<class 'builtins.Listener'>
async
<class '_asyncio.Task'>
async calling sync..
sync
<class '_asyncio.Task'>

After a bit more exploring, all methods belonging directly to the ngrok module have the same behaviour.

Either:

• the type hints should be updated to reflect the true return types
• explicit async methods should be implemented (ex. forward_async)

The second option is a better solution.
As my example hints at: the sync function calls forward and gets back an awaitable.
This is problematic because the sync method cannot await the listener. This means that it has to be refactored into an async function. It also means that the caller of sync either needs to be async itself, or run the function explicitly with asyncio.run() (or similar).

Edit: On reflecting on this, it might be a bug in how the code is detecting whether it should return an awaitable or not. That isn't a question I can speak to intelligently.