FileMaker 16 removed the zoom controls and mode dropdown that used to be at the bottom left of the window. The obvious workaround is to add a Bottom Navigation part to every window, with zoom and mode buttons, but that gets kind of tedious to implement after the first few hours (if you have lots of DBs and layouts).
A better solution would be if it were possible for users to add zoom controls and a mode dropdown to the Toolbar. The Toolbar is already user-customizable, and customizations apply to every DB the user opens, and are maintained across sessions, which makes it perfect for this purpose. The zoom buttons could just be buttons, + and -, labeled Zoom. The Mode could be a dropdown-button, like Manage. I'm not suggesting these should be in the Toolbar by default, just that it should be possible for users to add them if they want (via Customize Toolbar).
(Granted, the best solution would be to revert to FileMaker 15 behaviour, since that would allow the controls to work in Layout mode as well, but I don't think that's realistic. Adding a few optional buttons to the toolbar seems like it should be easy to implement, and would solve most of the problem.)
NB I'm suggesting this for the Mac client software; I don't know if this problem/suggestion would apply to Windows.