How to get YY in Develop Module

Hi, grateful for any advice on how to get YY to compare before and after.  I read that it is only available in the develop module but it doesnt appear on my screen.  I can compare with other photos (XY) in the library but the YY button is noticable for its absence.

When I select library, at the bottom underneath the photo there is grid view, loupe view, then compare view XY followed by various other selections.

When I then select Develop or press D these all disappear, leaving only stars, colours, zoom etc (everything ticked on the view modes arrow drop down on the right)

After hours of searching I eventually found a solution in the 'View' (at the top) 'before and after' then 'Left/Right' with a 'Y' shortcut.  Has this replaced the YY?

Thanks