SOLVED:
The above did not help. Then I simply installed sklearn from within Jypyter-lab, even though sklearn 0.0 shows in 'pip list':
!pip install sklearn
import sklearn
What I learned later is that pip installs, in my case, packages in a different folder than Jupyter. This can be seen by executing:
import sys
print(sys.path)
Once from within Jupyter_lab notebook, and once from the command line using 'py notebook.py'.
In my case Jupyter list of paths where subfolders of 'anaconda' whereas Python list where subfolders of c:\users[username]...