Looks like clickbait to me.
OPFS is not a real filesystem. It's basically indexedDB with filesystem-like characteristics. It does not give you access to the host filesystem.
The File System access API can do that, but it needs the user to grant permissions for each file or directory accessed separately, and this permission cannot be persisted between sessions. So it is a constant nuisance and cannot be used to create an ergonomic mostly local web application.
The File System access API can do that, but it needs the user to grant permissions for each file or directory accessed separately, and this permission cannot be persisted between sessions. So it is a constant nuisance and cannot be used to create an ergonomic mostly local web application.