I can’t load it either. I’m not sure what the issue is, the samples appear to load but I get no sound either in the plugin version or the standalone version.
I’d recommend trying another sfz file just to test sforando and reassure yourself you aren’t doing anything wrong.
https://www.pianobook.co.uk/library/ab-chase/ is a piano and has 2 sfz files you can try that I have checked and do work load into sforzando.
Then you can look for other sfz files on pianobook (I make it 76 sfz files on this site) or elsewhere.