why the symmetry option cant select in erase mode?

I am not an expert, but it seems to depends on the kind of shapes you are applying
See with mine, the options hows. However, with the wedge shape, it doesn't!

Try to see if it shows for you with other shapes, just in case.

Ignore me: It works with all shapes, but the option at the bottom of the screen (the one I use more often) seems glitching, the right clicked options works for me.