What is this Overlay Application and How can I get rid of it?
Thanks for adding the comment. This looks like the "Navigation Dock" feature of Huawei's EMUI. Because these Chinese system skins will include all features that are included with an iPhone.

You will find the option to disable if you search for navigation dock in your settings app. 

It should also be somewhere here (varies slightly per device). 

Settings > Smart Assistance > System navigation > Navigation Dock. 

Let's see how that goes.