What is not true about isosceles trapezoid:
The diagonals don’t have the same length.
The base angles don’t have the same measure.
The segment that joins the midpoints of the parallel sides are not perpendicular to them.
Opposite angles are not supplementary, which in turn implies that isosceles trapezoids are not cyclic quadrilaterals.
The diagonals don’t divide each other into segments with lengths that are pairwise equal.
Hope this helps! :)