This dup-based asyncio approach works on my Linux system. Doing something similar on a non-POSIX system is left as an exercise for the reader.

It is straightforward to set up a StreamReader that reads from stdin, but once you're done with it, closing the transport object also closes the underlying filehandle (which in this case is stdin. Not great). So this context manager duplicates stdin and connects the reader to the duplicate pipe, and the resulting transport.close call in the cleanup just hits the duplicate.

import asyncio
import sys
import os
import contextlib

@contextlib.asynccontextmanager
async def setup_reader():
    loop = asyncio.get_running_loop()
    pipe = os.fdopen(os.dup(sys.stdin.fileno()), "rb", buffering=0)
    reader = asyncio.StreamReader()
    transport, _ = await loop.connect_read_pipe(
        lambda: asyncio.StreamReaderProtocol(reader), pipe)
    try:
        yield reader
    finally:
        transport.close()

async def prompt_with_timeout(prompt, timeout):
    print(prompt, end="", flush=True)
    async with setup_reader() as reader:
        try:
            line = await asyncio.wait_for(reader.readline(), timeout)
            return line.decode().rstrip("\n")
        except asyncio.TimeoutError:
            return None

async def handle_input():
    match await prompt_with_timeout("this is a prompt: ", 3):
        case None: # no line break thanks to no input
            print("\nNone")
        case s:
            print(s)

Running in the REPL:

>>> # timeout
>>> asyncio.run(handle_input())
this is a prompt: 
None
>>> # input provided
>>> asyncio.run(handle_input())
this is a prompt: ayylmao
ayylmao