There is a conflict in the casing
C:\Users\Ruben|desktop\reactapp\test….
whereas the nodemodules is looking for C:\Users\Ruben|Desktop\Reactapp\test….
This is a windows specific problem, and previously react would have run the app regardless of this difference. Not anymore it seems.
The solution I used was to locate the folder and open with code; that ensures that the path matches directly with what is stored in node modules