Okay, so that means there's some code somewhere that has a lowercase "lib".

If you change it back to "Lib", can you do "python -m pip"? If that works, but a direct "pip" does not, it'll be an issue in pip (or a dependency), as those executables are generated by them.

There are likely many places where we rely on case-insensitivity throughout the codebase though, and certainly a number of places where we unconditionally casefold on Windows before doing comparisons. It's going to take a decent amount of time to track these down, and may not always be feasible, but if we can start enumerating them then it's worth making the fixes.