Here is the output:
Try bootup smallupdate
/usr/syno/sbin/synoupgrade: unrecognized option '--bootup-smallupdate'
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--auto
--auto-dsm=DSM_PAT_VERSION
--check
--check-dsm=DSM_PAT_VERSION
--download
--start
--patch ABSOULATE_UPGRADE_FILE_PATH
--cksum
--auto-smallupdate
--check-smallupdate
--download-smallupdate
--check-pat ABSOULATE_UPGRADE_FILE_PATH
--migration-check-pat ABSOULATE_UPGRADE_FILE_PATH
--prepare-upgrade-files-to-root
--prepare-smallupdate-downloaded-info ABSOLUTE_PATH_FOR_PREPARATION
--get-smallupdate-install-files-path
Failed to synoupgrade --bootup-smallupdate [255]
Exit on error [6] bootup-smallupdate failed...