The list on the left of the window which displays the rooms and personal direct messages you are part of is handy, but it would be incredibly useful to be able to collapse or hide that list. This would be handy for scenarios where a power-user may want to cause the Webex app to take up a tile on their screen instead of making the window wider or taller.
Currently, in such a scenario, the elements of the app take up a large amount of space within the application window which makes it difficult to focus on the conversation at-hand when tiling the Window into a section of the screen for multi-tasking purposes. Being a Linux poweruser to some extent myself, I appreciate when software allows me to hide elements that don't always need to be taking up space so I can continue to use it even when it is not maximized.
This, however, isn't limited to Linux. Some users on Windows may use tools such as Microsoft Powertoys to accomplish many of the same things that a Linux poweruser may wish to accomplish with their personal workflow including advanced window tiling. I believe there is also a similar tool for macOS users.
I would love to see a feature implemented that would allow the user interface of the main window become more minimal by having elements such as toolbars hidden when they are not needed with associated, configurable keybindings to "unhide" them when they are needed.