Collapse the parts of the board you are not using
Done holds every request the board has ever finished, and it takes a third of the screen. Collapsing it is not a change to the board. It is a change to your view of it, and nobody else sees it happen.
Steps
- On the board, find the chevron at the right edge of the first or last column's header and select it (its label reads Collapse column). From the keyboard, Tab to the chevron and press Enter or Space.
- To bring the column back, select the chevron on the collapsed strip (Expand column). After a keyboard collapse the focus is already on it, so the same key undoes what it did.
- With swimlanes on, select the chevron in a lane's header to fold the whole row away (Collapse lane), and again to open it (Expand lane). It answers the same two keys.
What you should see
A collapsed column shrinks to a narrow strip showing its name and its count as vertical text. What the remaining columns do with the space depends on where they already are: if they were sitting at their minimum with the board scrolling, the scroll gets shorter; if there was room to grow, they widen into it, up to the width a column stops growing at. The strip is still a drop target, so a card can be dragged onto a collapsed column without expanding it first.
A collapsed lane hides its columns; the lane header, its name and its count stay visible, so a row you folded away still tells you how much is in it.
Both choices are stored per user and per board, in your own Azure DevOps. They are still there the next time you open that board, and they change nothing for anyone else who opens it.

Notes
Only the first and last column offer the chevron, the same restriction native boards apply, though a column that is already collapsed always offers to expand. Collapsing a column collapses it in every swimlane row at once, since it is one column. Two things worth knowing: a collapsed column that is also configured as split does not accept drops, and a dependency arrow is not drawn when either of its two cards is inside a collapsed column or lane.