Some views no longer available in the topmost button bar
In earlier versions it was pssible to enlarge the topmost button bar with the view buttons. Since version 9 the bar is fixed and cannot be altered by the user. Some of the views (such as the light table) even do not have shortcuts which also cannot be customized. The user now has to choose from the drag down menu which is not convenient and a step back compared to earlier versions in terms of usability.
Thank you for sharing this feedback. We will review this enhancement for future releases.
Grant Robertson commented
The Reference Manual for version 9.0 (Last updated 10/15/2018) still says that you can "Drag the vertical bar to the left of the workspace buttons to show more or fewer buttons." Because the manual says you can do it, but you can't, this isn't an "enhancement." It is a bug.