I have followed up to the part with the lecture mentions turning on clipping in the mirror funtion.
I am in Blender 4.1, and for me the vertex and its mirror work the same when I do not have clipping enabled. When I enable it the gap between the vertex and its mirror still appears. They are not “stuck together”.
It does have an effect in that with clipping enabled the vertex and its mirror are no longer able to overlap. Am I missing something or is the a change in my version?