After months of proper operation, my per-user Python install started to error out when I attempt `python -m venv .venv` with 

"Error: Command '['C:\\Users\\kesh\\test\\.venv\\Scripts\\python.exe', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 101."

Following the StackOverflow solution, I reinstalled Python for all users and it was working OK. I recently looked into it deeper and found the root issue in the function PC/launcher.c/run_child(). The path to the "...\Python\Python310\python.exe" contains a space, and the CreateProcessW() call on Line 811 is passing the path without quoting the path, causing the process creation to fail.

I fixed my issue by using the Windows short path convention on my path env. variable, but there must be a more permanent fix possible.

Here is the link to my question and self-answering to the problem:

https://stackoverflow.com/questions/71039131/troubleshooting-the-windows-venv-error-101