Sounds like you may not have fully understood the trick/details in the top-up approach, and that's perfectly OK - it is a hack cleverly combining the effect of 2 commands and 2 flags. Let me try to explain using your situation as example:
I suggest you execute a copy command like this every 15 minutes:
rclone copy --max-age=1h --no-traverse --update --use-server-modtime --verbose /path/to/files EncryptScaleway:
--max-age=1h
tells rclone to only compare files with "modified time" within the past hour. Used by itself it will make a full directory of both source (/path/to/files) and target (EncryptScaleway) and then filter those based on modification time before comparing them, so no reduction in your egress by using this flag alone.
Important note: It will not detect rename and deletion of old files. It also will not detect if you copy an old file into the local folder (assuming an unchanged modification time older than --max-age). That's why we also need a daily job to catch and sync these; that job is at the end.
You can test the effect with this command: rclone lsl --max-age=1h /path/to/files
I have included some overlap to compensate for scheduling variances and network glitches causing single job failures. Adjust as you see fit, it could probably be 24h unless you create a lot of new files during the day.
--no-traverse
tells rclone to compare the entries in the source directory listing one by one to the target directory. Used by itself it would cause a one-by-one look up of (almost) all the entries in your target directory and be quite costly in time, egress and API cost. It is far more efficient to download/traverse the entire directory listing in one sweep, that's why it is the default.
--max-age=1h --no-traverse
tells rclone to first look in the source for any files modified in the past hour and then look up only these (few) entries in the target directory. Now this is fast and cost effective if you only have few new/modified files and a lot of files in the target.
Now you just need to run your original sync job periodically (e.g. every 24 hours) to catch the situations mentioned above:
rclone sync --fast-list --update --use-server-modtime --verbose /path/to/files EncryptScaleway:
Hope you now have a good understanding of the benefits and limitations of the top-up approach.