I am using python 3.8.11 and following is my project structure

test-project
|
|--- package_1
|   |
|   |-- module_11.py
|
|--- package_2
    |
    |-- module_21.py

I have following snippets inside the modules

# test-project/package_1/module_11.py
def my_func_11():
    print("Hello from module_11.")


# test-project/package_2/module_21.py
from package_1 import module_11

module_11.my_func_11()

When I execute module_21.py while in test-project directory it works perfectly fine on Linux (RHEL 7.9) but same project throws ModuleNotFoundError on Windows.

Tried adding __init__.py and importing respective package modules in both directories package_1 and package_2.

I know this can be fixed by adding project path to sys.path but I am more concerned about why it does not work on Windows.