They don’t!
As standard, local files are synchronized to Murena cloud, and accessing local files is then enough as they are identical to cloud.
It’s you who want to access directly cloud space from Files app, making things more complicated than they need to be 
If you don’t want to use the built-in synchronization mechanism, you’ll then need to rely on third-party like Nextcloud app or web browser. Seems pretty fair to me.