Hmmm interesting
So I have a map (it is a map view as it is open) called Validation and it has some selected point features in it:
I also have a layout called Crimes_Layout. This layout has a single Map Frame. That map frame is looking at the Validation map (notice the same selected features in the layout...):
When I click on my layout and I then run the code in my notebook, which I supplied previously, the map inside of the map frame (which is inside of my layout) zooms to the extent of the selected features in my map:
I think the order in which you click on the layout tab and then the notebook is important.
Also to get this work on your machine just try to keep it simple to begin with. Understand the workflow which is required to get the map in the layout to zoom to the extent of the selected features...
I hope this works for you.
Many thanks ed