Right now, the Files App supports uploads/downloads into a single view of a directory.
There are already possibilities for using per-user remote directories with Rclone (NextCloud, OneDrive, etc.). This seems to call for a two-panel interface like GlobusOnline, WinSCP, or MidnightCommander, with one view local, and the other either local or remote.
Currently, it is possible to use the Move/Copy button to transfer a file from the currently viewed directory to another. However, it is not so easy to navigate in the target/second directory. Seeing both source and target directories would be more natural.