In order to void the warrantee, they have to show that the product CAUSED the failure. If the engine or transmission were to fail under warrantee, it would be very hard to blame a paint kit.
I don’t know what spray you are talking about, there is one but your post goes to a door edge protector, but on that page, one of the other “also viewed” items was a paint protection film that is applied to the surface to be protected.
These film paint kits, which are a clear plastic or vinyl film that adheres to the paint are commonly sold for the front bumper and leading edge of the hood for protection from small stones and bugs. It works but it can be a little too pricy for me. Custom cut kits can cost over $1000 installed.
There is a spray on version of this at Walmart that costs about $30. I haven’t tried one because quite honestly, I’m just not that anal about the appearance of the car. I keep it clean, but since I don’t enter it into car shows, I don’t worry about little scratches and paint chips. I keep my vehicles for up to 20 years or more and I haven’t has a rust through yet, but I don’t live in the rust belt.