I have just upgraded to 2020 after a rather long pause, and am therefore spending a good deal of time in Z Classroom. For the life of me, I cannot locate transparency, and I believe some of the classes are on an older version. It used to be on the bar to the right, correct? _And I am trying to make transparent the masked areas, something I believe I used to do in an older version.
The Tool Transparency and Ghost functions which are modeling aids are located on the right side of the default UI canvas viewport, but also located in the Transform menu by default.
BPR render time transparency is controlled in several locations: Render> Render Properties> Transparent, Render > BPR Transparency, and Tool> Display Properties> BPR settings.