Are all lines of symmetry also diagonals? !

I think no, now all lines of symmetry are diagonals because it can also be horizontal and vertical.
Symmetry is also known as proportion; anything that is equal or proportion with each other.
Let’s have an example:
A square
=> in getting the symmetry of a square, we need to draw a 2 diagonal lines to each edges.
=> we can also draw 2 perpendicular lines that bisect to the edges of the square and it also provide an equal parts or proportional parts.