I am not much familiar with the environment you have, however, I suggest you check the location of the "site_packages" and make sure that the pip is installing in the same path of the "site_packages" that you are mainly using to install your packages. Also, you may consider creating a Python virtual environment in which you install all your packages in and ensure that it is activated while executing your code.

if you connect from mobile device to http://192.168.1.3/HelloWorld.py on server with CGI then code should be executed on server, not on mobile device. If CGI doesn't work then server may try to send code as normal file and then mobile mdevice ay try to run it locally but it is wrong - CGI server should run code on server.

At start I would put code in subfolder cgi-bin to run it as http://192.168.1.3/cgi-bin/HelloWorld.py because most CGI servers as default run code only in this subfolder.

On Linux script would need shebang

#!/usr/bin/env python

in first line and it should be executable

chmod a+x script.py

CGI has also some rules how to generate data which it will send to client. It may need at start extra information for HTTP protocol - and using only print("Hello World") may generate wrong data and it may have problem to send it. You should have it in any tutorial for CGI scripts. See module cgi

To run Python's code Apache needs module mod_cgi, mod_fcgi or mod_python

mod_cgi and mod_fcgi can run scripts in different languages: Python, Perl, Ruby, etc. and even Bash, PHP or C/C++/Java

Python3 has standard module http which can be used also as simple server

python3 -m http.server --cgi 

and it will serve all files in folder in which you run it. And it runs files from subfolder cgi-bin/ - see doc: http

in my case, the modules were installed in a user env, vs the machine's env. i just run:

sudo -H pip3.7 install mako

The -H says to sudo to install the module in the root machine directory vs user directory who run the command ...

this is because Apache cannot access/read personal user's files.

These two optiones worked for me: sudo apt-get install python3-pandas

or

sudo -H python3 -m pip install pandas