Upload only updated/changed files

If i do a cronjob every 2 hours for 0 22 * * * /usr/bin/rclone copy source/a/b/ dest:dest/a/b/ will that skip unchanged files and only upload changed files?

Yes, rclone copy will skip identical files (the equality check depends on the remotes, as it will use a hash in some and a timestamp in others) automatically.