Allow me to return to the interface that I've become accustomed to.
I absolutely hate updating Adobe Illustrator. This new Illustrator interface update is infuriating. The workflow that I've developed over years of working with this product is broken. I don't understand how anything works and I spend more energy wrestling with an interface that a just a short while ago was transparent to me than I do in the actual creative work that I am paid for. I'm sure you're proud of your work. I'm sure that you've tested it with naive users (I hope!) maybe even some seasoned users. But recognize that every time you make radical changes to the layout you're hanging a significant portion of your dedicated user base out to dry. Disruptions in my workflow like this make it more reasonable to spend time learning tools like Axure and Sketch that are more powerful, but that I normally keep in the background because I'm quicker with Illustrator. When you take that away you open the door to reevaluation.
To revert to the older workspace (without Properties panel), please choose "Essentials Classic" from the workspace menu on top-right corner of the app window.