hello and welcome to the forum,
i have never used that module, but i took a quick look at the source code.
the mount point is hard coded on line 36.
CLOUDROOTMOUNTPOINT=$HOME/cloud
https://github.com/piyushgarg/rclone-mount/blob/master/binary/rclone-mount
as per the documentation, mounting to a sdcard is not permitted.
" Mount point can not be placed in /sdcard/"
https://github.com/piyushgarg/rclone-mount#known-issues
not a linux expert, given that rclone can mount to a sdcard, i think that is a limitation of the module.