How do I open files using the shortcut thing?

Sorry I don't even know what this widget is called, but I've been using it in RubyMine and GoLand for about 7 years. Today it stopped working.

I realize we all have custom keyboard shortcuts, but please work with me on this.

Normally to open an existing file in my project, I type Command-Shift-O (on a mac) and a bar comes up where I start typing parts of the relative path to the file, and get presented with a list of matches. I can press return to start editing the first file in the list, or double-click on the path I want.

I don't even know what this widget is called. I inherited it from a plist/xml file from some people I worked with in 2016 and kept it, even when I changed jobs. I tried mapping `Main menu | Navigate | File…` to Command-shift-O, but that does nothing.

I don't know why this binding disappeared – it worked last Friday (we had a big power failure and internet outage for 3 days). But I've already had two other computer things stop working for me this week. One was due to someone pushing an insufficiently tested brew update; the other my Windows box deciding I no longer needed access to the file system. So can someone help me solve this one?