- login to Admin Console
- go to Website & Content → Structure & Data section
- create new section with empty "Description" field and "Promo Block Group" field set to "Default Grooup"
- remember it's "Modified On" field value as seen in the grid (e.g. 2020-06-04T12:39:05+0300)
- open that category for editing
- write something in description field
- save changes
- confirm, that "Modified On" field value was changed (if you change data too quickly, then change could be in seconds, that aren't shown)