You can utilise ignore patterns to sync files on demand but the user experience isn’t the greatest, especially on a touch screen device, as you need to modify the patterns by hand.
I also use rclone on my cell.
How are you getting rclone to be recognized as a drive in the local File Explorer?
I downloaded an app from the Android store called files and it has the ability to see the rclone cloud drive.
I have both RCX and Round Sync too. It is a fork of rcx that is a bit newer.
It probably works on Windows Linux and Mac with rclone. I haven’t tried that yet but I am curious and having it available on Android would be spectacular.