The ssh input is very slow

I'm making trzsz, which similar to lrzsz.

The trzsz wraps ssh in cmd. The download speed is fast as expected, but the upload speed is very slow.

Troubleshooting steps

1. Download trzsz.exe from trzsz_windows_amd64.zip, or make it yourself.

git clone https://github.com/trzsz/trzsz-go.git
cd trzsz-go
GOOS=windows make

2. Add trzsz.exe before ssh, login to a server. e.g.:

.\trzsz.exe ssh yourname@127.0.0.1

3. Install trzsz on the server. Require the test version 0.2.111:

sudo python3 -m pip install --upgrade -i https://test.pypi.org/simple/ trzsz==0.2.111

4. command trz to upload a file.

5. The trzsz.exe will read the file and send the content to the ssh stdin.
   The trz will read the content from stdin and save it to the server.

"OpenSSH for Windows" version

V8.9.1.0p1-Beta

Actual output

The upload speed is about 24 KB/s.

Is the ssh process having a small buffer, and the input data from stdin is not processed in time?

Expected output

The upload speed should be above 2 MB/s, same as on ubuntu.

Start by reproducing the upload through trzsz.exe ssh on Windows with OpenSSH V8.9.1.0p1-Beta, then compare stdin throughput with Ubuntu. Done when upload reaches the expected rate and the behavior is covered by a repeatable test or benchmark.