lsl doesn't recognize --rmdirs.
rclone delete remote:/backup --min-age 3d --drive-use-trash=false --rmdirs -v removes the content but cannot delete the directory.
I think the reason is --rmdirs checking the folder before deleting the files that is why it cannot remove the empty directory after wiping out the files.
My workaround is;
rclone delete remote:/backup --min-age 3d --drive-use-trash=false && rclone rmdirs remote:/backup --drive-use-trash=false
since delete --rmdirs doesn't work in my case.