This bug seems to have been caused by https://salsa.debian.org/cpython-team/python3-defaults/-/commit/8e243207fee371a7335674fc77db63044b62cb29
It migrated from imp to importlib, but importlib doesn't imply importlib.util -- you cannot and AFAIK never have been able to import the top-level package and assume the nested modules are available. That being said, it did work for me in my (non-Debian :P) 3.11 environment, purely because I had a .pth file that caused importlib.util to be imported at startup. (It is the stock setuptools one for namespace packages. You can isolate the interpreter a bit with -IS to catch this.) So a similar problem may explain why this wasn't caught during local testing. It probably makes sense to generally test this sort of thing with minimal packages installed, because sneaky .pth files will cause you issues all the time.
