I would like to know if I can create an python API that receives username and password from a Google user and has access to Google services from that user.
ex:
User gives me google email and password and I can move files between user GCP buckets
If there is no way to do this directly, I would like to know ways to perform this operation without a frontend, only with the user's email and password
It is not possible to retrieve the password for a Google Account via an API.
Your question:

I would like to know if I can create an python API that receives
username and password from a Google user and has access to Google
services from that user.

Yes, you could create a Python API that asks the user to enter their username and password. That is easy to do via an HTTP form.
However, even with the username and password, Google security would quickly block the account. All authentication is browser-based for user identities and requires a human to interact with the browser.
Python API using User Account to use User GCP Services (Storage, Engines, etc)