Privacy screen on the bathroom window

our site manager says that a film would not be good for our windows ("float glass").

Why should the film not be good? Float glass is standard for glass panes. What warranty for what?

Such nonsense...

I am just wondering how a foil like that is supposed to damage the glass or affect the building physics in general? I have had foil on three windows for partly 10 years, nothing happens.

our site manager thinks that a film would not be good on our windows ("float glass"). Can anyone confirm this?
(Our general contractor uses the trump card "warranty").

Apparently, "warranty" is being used here as an inappropriate trump card to possibly exclude warranty?
Then you would live in the house for years without knowing whether you are allowed to do this or that without voiding the warranty, from the wrong wallpaper quality to the choice of possibly the wrong window cleaning agent...? Oh dear!
I would be interested in the technical explanation of this problem that the general contractor seems to see here.
We have repeatedly applied films on various windows and I have always been positively impressed by how good it can look. It has never caused any damage to the glass. What damage, anyway?

My mother once improperly applied film for shading on the inside of an approximately 2.5m x 1.2m window. Full south side, no external shading. The pane cracked. Probably a small mini greenhouse layer formed between the film and the pane and was able to heat up so much that the pane simply couldn't withstand it anymore.

I don't want to say that this has to happen, but it can apparently happen.

On panes exposed to a lot of sunlight, I would only apply opaque films from the outside. (And if something should happen, remove the films beforehand before the service comes).

It seems "unlikely" to me that the film should be the cause. The pane might have cracked for other reasons as well? I personally find "real" frosted glass panes "somehow nicer", but film is hardly distinguishable and more versatile.

Glass panes can even crack with improperly installed pleated blinds/shutters. Or with poorly mounted roller shutters that are not fully lowered. Whenever something is installed close to the glass, heat buildup with large differences compared to the rest of the pane can occur. Sometimes it then cracks.