Reported in slack. This error occurs when using 4.2.0 with pymongocrypt < 1.3. The fix is to upgrade pymongocrypt too:

I have just upgraded to the 4.2.0 driver and I now get an error with CSFLE when creating DEKs:

Traceback (most recent call last):
  File "/opt/homebrew/lib/python3.9/site-packages/pymongo/encryption.py", line 76, in _wrap_encryption_errors
    yield
  File "/opt/homebrew/lib/python3.9/site-packages/pymongo/encryption.py", line 622, in create_data_key
    return self._encryption.create_data_key(
TypeError: create_data_key() got an unexpected keyword argument 'key_material'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/brett.gray/Documents/Dev/Crypt/csfle_6.py", line 335, in <module>
    main()
  File "/Users/brett.gray/Documents/Dev/Crypt/csfle_6.py", line 225, in main
    employee_key_id, err = get_employee_key(client, kms_provider, provider, namespace, employee["dekAltName"])
  File "/Users/brett.gray/Documents/Dev/Crypt/csfle_6.py", line 158, in get_employee_key
    employee_key_id = client_encryption.create_data_key(kms_provider=p, master_key=master_key, key_alt_names=str(id))
  File "/opt/homebrew/lib/python3.9/site-packages/pymongo/encryption.py", line 622, in create_data_key
    return self._encryption.create_data_key(
  File "/opt/homebrew/Cellar/python@3.9/3.9.13_2/Frameworks/Python.framework/Versions/3.9/lib/python3.9/contextlib.py", line 137, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/opt/homebrew/lib/python3.9/site-packages/pymongo/encryption.py", line 82, in _wrap_encryption_errors
    raise EncryptionError(exc)
pymongo.errors.EncryptionError: create_data_key() got an unexpected keyword argument 'key_material'

This did not occur with 4.1.1
Any ideas why the key_material is causing issues if I am not declaring it and it is optional?
...
Wan helped me with this, I needed to upgrade pymongocrypt to 1.3.0.

We should make these kinda of errors easier to debug. The problem is that pip does not warn about dependency conflicts for optional deps like pymongocrypt.