Turn on the Kanban backlog feature for the board is correct.

Enabling the Kanban backlog gives you a separate backlog area that stays out of the main board columns and that prevents the planning column from becoming overloaded. The backlog area is designed to hold items you are not actively working on so you can keep the planning column focused on items you intend to refine or start soon.

Create a new workflow status and add a column then leave that status unmapped is wrong because adding an unmapped status and column changes your workflow and can hide or misplace issues. It also complicates workflow management and is not the intended way to separate backlog work from active board columns.

Modify the board filter to hide issues in the planning status is wrong because filtering will remove issues from the board entirely for all users and can break visibility and reporting. Hiding items is not the same as separating a backlog area and it is a blunt instrument compared with the backlog feature.

Add a distinct backlog column to the board is wrong because putting backlog items into a regular column makes them part of the board flow and can distort work in progress and metrics. The Kanban backlog feature is the correct mechanism to keep backlog items out of the board columns without altering workflow semantics.

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