find_spec() has superseded find_module() since Python 3.4.

New changeset a7ff6df60c05e1b69fca743573b1e118bebf121d by Brett Cannon in branch 'master':
bpo-42134: Raise ImportWarning when calling find_module() in the import system (GH-25044)
https://github.com/python/cpython/commit/a7ff6df60c05e1b69fca743573b1e118bebf121d

Brett, would you accept a PR that changes the changelog entry to contain the ".find_spec() not found; falling back to find_module()" message, for better search-ability? I needed to use grep + git blame to be able to find out what's going on.

Also, could you please explain how to migrate to find_spec() in https://docs.python.org/3.10/whatsnew/3.10.html#porting-to-python-3-10 ? I'd do that, but I don't know yet what is the proper way.

See also bpo-43540 "importlib: Document how to replace load_module() in What's New in Python 3.10".

> would you accept a PR that changes the changelog entry to contain the ".find_spec() not found; falling back to find_module()" message, for better search-ability?

Sure!

> Also, could you please explain how to migrate to find_spec() in https://docs.python.org/3.10/whatsnew/3.10.html#porting-to-python-3-10 ? I'd do that, but I don't know yet what is the proper way.

The problem is it will possibly vary from class to class. You can probably get pretty far with https://docs.python.org/3/library/importlib.html#importlib.util.spec_from_file_location or https://docs.python.org/3/library/importlib.html#importlib.util.spec_from_loader depending.