Environment Variable in MSIX Using PSF

Abhi211 You didn't specify the source of the PSF being used.  Sometimes that matters, but probably not in this case.  Here is what is obvious from the post:

In the json, the name of the fixup file should not include the bitness (architecture).  It should just be listed as "EnvVarFixup.dll".  The PsfRuntime will look at the bitness of the application (x64 in your example) and then try to load a file with that added in (EnvVarFixup64.dll).  Since you made the json by hand, I'm guessing that you may have put in the files by hand, so make sure that version of the dll is in the package (it never hurts to put both bitnesses in when you don't know the app).