I went through all posts of this thread for the past two days, and I learned a lot!
So thank you to everybody

I first had an issue with importing hou module, but it was fixed thanks to those steps:
- Set $HFS to Houdini's installation folder
- Set $PATH to $HFS\bin
- Append $HFS\houdini\python%d.%dlibs to sys.path
All of that is already well explained in the documentation, but I still had weird issue with it: it couldn't load the DLL.
The main issue was found thanks to this:
rvinluan
I think the problem might be the Python interpreter itself. It looks like it is built with an older compiler version so it probably cannot import the compiled _hou module or its library dependencies because they are built with MSVC 2015.
The reason being that I was excuting my Python script with Python 3.9.5.
BUT I had Houdini with Python 2.7 installed. So I installed Houdini with Python 3 instead.
After some tests, and thanks to rvinluan's post previously mentionned, I understood I also needed to match my Python version to the one shipped with Houdini.
This version is actually Python 3.7.4.
So I downgraded my Python from 3.9.5 to 3.7.4 and everything works fine now!
So huge thanks to everyone on this post who helped me a lot understanding how all of this works together
