@harripy 
I've just looked through the Databricks SDK code and it looks like m2m auth is generating oauth bearer token to authenticate, that's why you see "access_token", but it's different from PAT (https://github.com/databricks/databricks-sdk-py/blob/68feadf82f12d387621704f2957d743bfc86f4bd/databr...).

So it looks like it's able to authenticate with Databricks through M2M and get access token. 
It's hard to guess what's the issue with the logs that you've provided.

What i suggest is to enable debug logging and paste the logs.
https://github.com/databricks/databricks-sdk-py/tree/68feadf82f12d387621704f2957d743bfc86f4bd?tab=re...