The Origin Private File System is coming to all browsers, Chrome, Safari, and Firefox. It's a universally agreed-on Web standard: https://fs.spec.whatwg.org/.
EDIT: I saw from your other comments on this post that Firefox has implemented at least the origin private file system part in nightly builds; that's useful info that I was looking for.
However the sqlite demo page says OPFS is unavailable for me in Safari https://sqlite-wasm-opfs.glitch.me/ ...unsure whether it only supports a subset of the APIs that the official sqlite build uses?