The input function should be input and not Input, rest of the code is absolutely correct. So, your code should be:

from ursina import *
from ursina.prefabs.first_person_controller import FirstPersonController


class Vovel(Button):
def __init__(self, position=(0, 0, 0)):
    super().__init__(
        parent=scene,
        position=position,
        model='cube',
        origin_y=0.5,
        texture='white_cube',
        color=color.white,
        highlight_color=color.lime,
    )

def input(self, key):
    if self.hovered:
        if key == 'left mouse down':
            vovel = Vovel(position=self.position + mouse.normal)
        if key == 'right mouse down':
            destroy(self)


app = Ursina()
for z in range(8):
for x in range(8):
    vovel = Vovel(position=(x, 0, z))
player = FirstPersonController()
app.run()

This code works, you can place a block with left click and remove a block with right click!