I'm not exactly sure how you're trying to get the photo onto your PC. Do I take it that you have your photos backed up to iCloud Photos, and that you're downloading from
www.icloud.com/photos onto your PC using a web browser? I wasn't clear on that when I read your original post, and for some reason I assumed there was a Mac involved, in which case you'd just export from the Photos app on the Mac, and choose 'Export as unmodified originals' when prompted.
But if you're downloading from the iCloud/Photos website, or exporting from the iPhone, I don't think this will work. In fact, from what I've read on the web, a lot of people are upset about the fact that Apple assume you're going to be working with your ProRaw files on a Mac, not a PC. For example, this thread:
discussions.apple.com
The thread is a few months old and things might have changed. Or, it's possible that the problem will be addressed in iOS 14.5. Perhaps someone else knows more about this than I do.