How to actually search all files in Visual Studio

I think you are talking about ctrl + shift + F, by default it should be on "look in: entire solution" and there you go.

So the answer seems to be to NOT use the Solution Explorer search box.

Rather, open any file in the solution, then use the control-f search pop-up to search all files by:

1. selecting "Find All" from the "--> Find Next / <-- Find Previous" selector
2. selecting "Current Project" or "Entire Solution" from the selector that normally says just "Current Document".

Press Ctrl+,

Then you will see a docked window under name of "Go to all"

This a picture of the "Go to all" in my IDE

One can access the "Find in Files" window via the drop-down menu selection and search all files in the Entire Solution: Edit > Find and Replace > Find in Files

Other, alternative is to open the "Find in Files" window via the "Standard Toolbars" button as highlighted in the below screen-short: