In Blender 2.31 S-X no longer works to mirror an object in the X-axis. Instead it constrains the scaling to the X-axis (positive values only). Surely this vital feature hasn’t been removed? There must be another way to do it, but I can’t find anything in the documentation.
switch to edit mode and press “m”
To flip an object in 2.31: in object mode, type this four keys S X - 1 (Scale, X axis, negative 1).