From answers to this question i've learned that the Lagrangian L$_1$ point of Venus is not stable, despite the almost circular orbit of the planet and the fact that it has no moon.

Nevertheless would it be possible that a flat structure, composed of panels made of Smart glass, perpendicular placed on the Sun-Venus axis right behind the L$_1$ point, seen from Venus, could stay there ?

A voltage applied to the electrochromic device would change the opacity of the glass material and thus would change the radiation pressure exerted by the sunlight.
Because of its place right behind the L$_1$ point this "solar sail" would have a slight pull from the gravity of the Sun and the radiation pressure could be changed sufficiently to counteract upon it.

The square structure would be surrounded at the edges by 45$⁰$ tilted panels to regulate that the structure would not deviate from the Sun-Venus axis.