Seems there are quite a few typos/copy-paste errors in the original steps-to-reproduce. Here are my steps on macOS:

$ ./python-build/python.exe -m venv 'aaa bbb'
$ source ./aaa\ bbb/bin/activate
$ pip
zsh: /Users/yen/tmp/aaa bbb/bin/pip: bad interpreter: "/Users/yen/tmp/aaa: no such file or directory

The result is similar on Linux.

Like Alex said, I don't think there's a portable solution, either, so here's a patch to warn users for possibly broken paths.

macOS kernel has another bug/limitation. In XNU, '#' symbol also breaks shebang:

$ ./python-build/python.exe -m venv 'aaa#bbb'
$ source ./aaa\#bbb/bin/activate
$ pip
zsh: /Users/yen/tmp/aaa#bbb/bin/pip: bad interpreter: /Users/yen/tmp/aaa#bbb/bin/python: no such file or directory

This is even confusing as the kernel thinks the interpreter is /Users/yen/tmp/aaa (everything after the first # is thrown away, see [1]) while zsh/bash thinks it's /Users/yen/tmp/aaa#bbb/bin/python. As a result, I add a warning for #, too

Some related discussions:
1. https://github.com/pypa/pip/issues/923 (pip does not support spaces in directories names)
2. https://github.com/pypa/virtualenv/issues/53 (Whitespace in root path of virtualenv breaks scripts)
3. https://github.com/pypa/virtualenv/issues/973 (bad interpreter error when creating virtualenv's in directories with '#' in name)

Adding venv maintainer and some macOS experts

[1] https://opensource.apple.com/source/xnu/xnu-3789.21.4/bsd/kern/kern_exec.c.auto.html, line 511