https://github.com/gabrielsroka/gabrielsroka.github.io/blob/...
it works on Chrome/Chrome for Android, but Brave requires a flag (brave://flags/#file-system-access-api), and i don't think Brave for Android supports it
One gotcha I ran into: browser support is still spotty. Had to implement fallbacks for Firefox and Safari users (they don't fully support it yet). Ended up with a hybrid approach - File System API for Chrome/Edge, traditional file input for others.
The permission model is also interesting - users have to explicitly grant access, which builds trust but adds friction to UX. Worth it though.
What are you using it for?
Makes sense if you think of all the ChromeOS work Google did.