Visual Studio "Open File" dialog: how do I change the default file extension?

Question

In Visual Studio 2019, I click on "Open File" (ctrl+O), but by default, the dialog box in the in the lower-right corner that tells VS which extensions to look for always says "Unit Test Files (*.cpp; *.h)", and I have to click on it and select "All Files (*.*)" to get it to display files that aren't .cpp or .h files. How can I change the default from "Unit Test Files" to "All Files"? I was unable to find any official documentation about this from Microsoft, but in previous versions of VS (e.g. VS2017) "All Files" was the default, so I assume it can be changed somehow