I'm not a linux expert either, unfortunately. Just playing around until one appears...
I think something like this should work. It will not be one rclone command, though, it will execute a rclone copy command for each unique directory at level proves/2021-01-01/folderA.
for f in $(rclone lsf --recursive --include="/2021-??-??/folderA/**" --files-only gdrive:proves | cut -d/ -f-2 | sort -ru); do rclone copy $f $(echo $f | cut -d/ -f2) --ignore-existing; done