Configuration for the Flagged field doesn't seem to be provided for Rapid Boards (Scrum/Kanban). Being able to configure the Flagged Field in the deprecated Classic Boards, posed a couple of advantages:

1. Users could configure different types of Flags (as suited for their usecases)
2. From the board configuration, it is easy to determine in which field the flag for issues are stored in JIRA.
3. Although the flagged field is not Locked by default, if it was deleted, admins could easily create and configure a new one etc.

Unfortunately, because this field is still unlocked by default, Rapid board users:

1. Would often delete it and then wonder where all their Rapid Board Flags are being stored.
2. Also, users who had been using their own/custom Flagged fields in Classic boards, before migrating to Rapid boards are prone to be even more confused about this because there is no longer an easy way to determine where this Issue flag data is stored like there was in the Classic Board Configuration Screen and Project Template configuration for classic boards.

This 'Flagging issues' feature should be configurable to some extent atleast in Rapid Boards as well