Does it make much of a difference here? It's passed by value for a one line function.

Fair enough on the double digits. Small correction - the numbers the kata specifies are 1-9.

Meh. Agreed - but the function name to complete is 'maps' so it seemed like a hint to use map. Either works fine.

This needlessly joins result all the time.

Nice. You should however choose another variable for 'sum' - you are shadowing Python's "sum".

This code looks ... shifty.

It's a generator expression. See https://peps.python.org/pep-0289/

Does not work for multiple digits, e.g. Fails with

'thr3ee one1 tw20nty twe2nty4for'

Neither does it work for e.g. with puntuation.
Also sorts everything twice. Would recommend against.

Fails with e.g.

['w', 'w', 'w', 'w', 'w', 'w', 'w']