> venv, on the other hand, doesn't, but keeps a reference to its original Python environment. That is, I think, the reason for the difference in behaviour.

But for example, using the system Python to create a venv (no nesting), packages installed system-wide (e.g. using a linux package manager) are not visible in the venv.  Or, as you note, nesting a venv into another works fine.  I don't understand why things would be different when nesting?

In any case thanks for the workaround.