Interesting, I hadn't considered that -- thanks. I was just having a look and it seems that right now, only Chrome and Edge (and Brave?) support that API. I'll keep an eye on it, because it doesn't seem like a viable option yet until Safari and Firefox also do.
It's possible to do this in Safari and Firefox as well, it's just that the experience isn't as seamless - instead of writing to the existing file a new copy will be downloaded.