The following is for Ubuntu systems, Windows has not been tested.
Python and Python are installed by default in Ubuntu, and by default the python command refers to Python. Therefore, when a Python script is set as an executable and executed directly from the command line, the system invokes the Python interpreter.
If you want to call the Python interpreter to interpret a Python script when it is being executed directly (e.g., typed at the command line), one way to do this is to modify the symbolic link so that the python command points to Python 3. This works on your own system, but it is not convenient if the script is to be executed on a different system. Another way is to specify the interpreter's location on the first line, as in shell scripts, e.g. #! /usr/bin/python3, so that running the Python file directly will invoke the specified interpreter.
The above method of specifying a Python interpreter in a Python file is all that I have shared with you.