Ok. I give up my quest for snapshots of /home and remain contented with backup on external HDD every few months.
Thank you all for inputs. Snapshot of /root (subvolume @) failed to restore 2 days back. Forced to clean install Manjaro again.
If there exist a fail-safe and step-by-step guide to (i) partitioning, (ii) Manjaro installation and (iii) taking/restoring snapshots, please share. Else people like me would learn hardway, stumbling on mistakes.