Opaque window property boundary

Questioner

I have a chalet that has been a residential property for a few years now. It was just placed about 30 years ago with the longest side exactly on the property line with the neighbours. It was not yet my property at that time. A large air conditioner was then placed in the (wooden) wall that hung about 50cm over the property line. In the meantime new neighbours have moved in and I have bought the chalet. The new neighbours were not happy with the air conditioner and have placed a fence along my chalet about 40cm away from it. Now I have had the air conditioner removed and wanted to place an opaque window in the resulting hole, but the neighbours do not agree and say that this is not allowed. So I should go for an uglier option, for them and for me, and that is just a wooden board against it. I thought that an opaque window was allowed by law?

Lawyer

If the window has a view of the fence, it doesn't even have to be opaque. If the window does have a view of the other property, then it does indeed have to be opaque.