The issue you're encountering with dbutils.notebook.entry_point.getDbutils().notebook().getContext().notebookPath().get() not returning a valid path that can be used in Python is known. This method indeed strips off the /Workspace from the start of the path and removes the suffix, which causes the Path.exists() check to fail.

To get the actual path of a notebook, you can prepend /Workspace to the path returned by getDbutils().notebook().getContext().notebookPath().get(). Here is an example of how you can modify your code to achieve this:

from pathlib import Path
import os

# Get the notebook path
notebook_path = dbutils.notebook.entry_point.getDbutils().notebook().getContext().notebookPath().get()

# Prepend '/Workspace' to the path
full_notebook_path = '/Workspace' + notebook_path

# Check if the path exists
print(Path(full_notebook_path).exists())

I actually think the major issue is that the above is undocumented and not supported. A supported and documented way of doing this would be much appreciated.