Hi,
My issue is solved by the following mount statement.
.\rclone.exe mount aws_s3:b1sqlsrv-backup F: --vfs-cache-mode full --volname \clouds3\share
After mounting the bucket, run the command within SQL management studio
BACKUP DATABASE SBODemoCN TO DISK = '\clouds3\share\SBODemoCN.bak';
and the database backup to S3 is done successfully.