for local files as well?
If that wasn't the case, then "HTML virus" would be a thing: I send you an HTML file and, if you open it, it read files from your hard drive and uploads them to my server.
I'm pretty sure Brave was blocking window.crypto but can't remember if it was on a file or over plain HTTP
Blocking crypto on file:// is not to spec, and testing above (https://news.ycombinator.com/item?id=34084526) none of the browsers do that.
All I remember is that I was developing the secret 'creator' code using Brave (my default unsecured browser) and at some point I had to switch to Safari (which I normally save for trusted websites only).
It's possible it was a red herring, and I switched browser but the problem was something else I did at the same time.
I do vaguely recall encountering some problem I didn't expect when I was making a tool contained in a local html file, but I dont remember which browser I was using at the time