Hi Hassan,
There is an 1:N relationship between Case and Note entity, or it can be said that our attachment is stored as an note record, and its content will be converted into base64 data in note's field called documentbody.
The connection between them is note has a field called _objectid_value, it point to case where the attachment added for.
So we should focus on Notes entity to get attachment, in my demo below, I got a attachment from a case record and saved it to Onedrive:
1. Attachment file in CRM

2. My flow configuration:
It will create a new file in Onedrive with its original name in CRM

3. Saved file in Onedrive

Regards,
Clofly