We have created a Document Type approval flow:

However "Save & Publish" remains an option when editing the node:

This essentially means it's possible to bypass the Workflow.
I would expect that with the "Flow type" set to "Exclude" it should not be possible to "Save & Publish", as the Workflow should not allow the user to "Approve" their own changes.
Umbraco Workflow Version 15.1.5
This item has been added to our backlog AB#54340