I’m new to the forum.
I buy this app for iOS and it’s very good.
I find the library icon, on the bottom left, in gray and not selectable.
I attach a screenshot
I have files both locally and in the cloud, and the librery are selected in the respective paragraph in settings.
Welcome to the forum!
In order to use the Library feature, you will need to add at least one Favorite and have this selected in the Settings > Library screen.
More info on adding Favorites can be found here.