Always when starting the installer it tells me to search for the folder.
That's not what is telling you. It's telling you where you want to install Vancouver, which can be anywhere you want and, by default, it's under the C:\Program Files (x86)\Addon Manager, which is a correct location, if you have enough space on C:
As all other scenery choose to install into V3
What do you with "all other scenery" ? If you are referring to other FSDT scenery installers, they used to force you to install into the folder of the simulator. Now, they all let you to choose freely, which of course is a big improvement so, if you are still seeing an FSDT installer forcing you to install into the sim folder, it means you are using an outdated installer for them.
If, instead, with "all the other scenery", you mean other sceneries from other developers, it simply means these other sceneries still have the same limitation of our old installers, and still force you to install into the sim, opposite to our new installers, which let you freely choose any folder and any drive.