so, not on a quest to hack new interop ways for fc...
but introspection of what is there.
your choice if you want to travel a muddy road during rain season or the smooth paved path.
recommendation is to go the paved path...
hard to tell if you understand how these things work or not (i'm leaning towards not).
anyhow, as mentioned you are going over the bridge to fetch water...
a) in your venv install thonny (editor), set the py-interpreter to the fc python (probably works, at least i have made it work, but that does not say that it will for you...)
b) forget your venv and python.org install, just fire up the fc-bundled python and everything is already there...
it is located in <your install dir>/bin, there you also find freecadcmd.exe, does not matter which one you use... (here you can pip install anything you want, assuming there is a compatible pip-package to fc-py)
c) use the gui console coming with fc (like most others do...)
d) try scanObjects macro, link on
Macros_recipes (code & scripting), dunno if it works...
e)
Debugging
fc simply is not a pip-installable package - it is a c application which happens to have a python bundled.
this is not a bug, it is by design, and your issue imho is a matter of you setting up the system at your computer...
python is and has always been cranky on path definition/discovery, as example, setting path in a session does absolutely nothing for a process call, since that is governed by environment (and for that your venv will do nothing, unless you tell it to, originating from the (hard) way you are approaching things)
a) as such is simple (if it works), but why ever do that? (and it really is b...)
e) is the most involved way, you might be lucky that it works, and then again you might not be... and if not you are on your own in sorting it out on your computer
c) you are up and running as soon as you have started the gui, and everything is available without you lifting a finger...
choice is yours what you want to spend time on...