Vertically centres the selected objects. If only one object is selected in Draw or Impress, the centre of the object is aligned to the vertical centre of the page.
Open context menu - choose Align - Centred (objects selected) (Collabora Office Impress, Collabora Office Draw).
On Align bar (Collabora Office Impress, Collabora Office Draw), click
Centred
To align the individual objects in a group, choose Format - Group - Enter Groupdouble-click to enter the group, select the objects, right-click, and then choose an alignment option.