Cloud services make use of Apple’s File Provider framework to integrate their files with the Finder (on macOS) or the Files app (on iOS).

While the framework technically allows a user to select the cloud service root in an open panel or file importer, the cloud service may not support it. For example, pCloud doesn’t support it yet. The workaround at the moment is to select a nested directory, or move all files into a single directory that can then be selected.